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Results for “EXTRACELLULAR SPACE”

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PubMed1996

Molecular mechanism of sleep regulation by prostaglandin D2.

Recent biochemical, molecular biological, and pharmacological experiments revealed that prostaglandin D synthase as well as prostaglandin D2 circulated in the ventricular system, subarachnoidal space, and extracellular space in the brain. Prostaglandin D2 then interacts with chemosensors or receptors on the ventro-medial surface of the rostral basal forebrain to initiate the signal to promote sleep. Prostaglandin D2 is, therefore, not a typical neurotransmitter but rather a 'neurohormone' or an 'informational substance' that circulates through the cerebrospinal fluid and transmits certain chemical messages to promote sleep. The mode of communication through the cerebrospinal fluid in the ventricular system and the extracellular space has advantages for global regulation of the brain to induce sleep.

Animals↗

PubMed2000

Development and repair of cataract induced by ultraviolet radiation.

BACKGROUND: Several epidemiological investigations show a correlation between cataract development and the dose of ultraviolet radiation (UVR) received. It is experimentally well established that exposure of animal eyes to UVR induces cataract. Most cataracts develop as a gradual increase in lens opacity. Despite this, current estimations of toxicity for cataract are based on the concept that cataract is a binary event. Moreover, current exposure limits for UVR are based on subjective inspections with slit lamp microscopy. PURPOSE: The first purpose of the present study was to determine a statistically defined maximum acceptable dose for ultraviolet radiation-induced cataract based on quantitative data of forward light scattering in lenses. The second purpose was to find possible explanations for light scattering by investigating the morphology and the refractive index distribution in the lens. The third purpose was to describe the development of cataract after UVR on the cellular level. METHODS: Six-week-old, female Sprague-Dawley rats received UVR unilaterally in vivo. The radiation from a high pressure mercury lamp was collimated, passed through a water filter and an interference filter or a monochromator (lambdaMAX = 300 nm), and projected onto the cornea. The exposure time was 15 min. The exposure dose ranged between 0.1 and 20 kJ/m2 and the animals were kept between 6 hours and 32 weeks after exposure. The extracted lenses were photographed and forward light scattering was measured. Other methods included light microscopy, fluorescence microscopy, transmission and scanning electron microscopy, freeze-fracture and microradiography. RESULTS AND CONCLUSIONS: From a long-term experiment, it was concluded that UVR-exposed lenses scatter light more than their contralaterals and that a higher dose induces more light scattering. After exposure to 5 kJ/m2, the mean forward light scattering remains unchanged between 1 and 32 weeks. Earlier observations, taken together with the current findings, indicate that the optimal time to detect low dose UVR-induced cataract is one week after exposure in rats. The intensity of forward light scattering increases exponentially with increased UVR dose between 0.1 and 14 kJ/m2. Based on this continuous dose-response, a method to determine a maximum acceptable dose to avoid UVR-induced cataract was developed. The statistically defined lower limit of pathologic light scattering is projected on the dose-response function. The dose corresponding to that point can be estimated and was suggested to be called the Maximum Acceptable Dose (MAD). Two low dose UVR exposures with 0 or 6 h intervals between the exposures produce the same degree of lens opacification. When the second exposure follows 24 or 48 h after the termination of the first, lenticular damage increases. Repair processes between 24 and 48 h after exposure appear to be sensitive to UVR, and an additional exposure during this time may aggravate cataract development. Lenses exposed to UVR grow more slowly than their non-exposed contralaterals. This decrease in lens growth was more pronounced with increasing dose. Low doses led to decreased water content in the lens whereas high doses led to swelling. At 6 months after low dose UVR exposure, no global change of the refractive index was found. However, local variations of the refractive index induce a subtle cortical light scattering. In vivo low dose UVR induces programmed cell death which peaks 24 h post-exposure and involves the entire lens epithelium. Dead cells are removed from the epithelium by phagocytosis. This leads to disintegration of the lens epithelium, associated with flake-like opacities at the lens surface. After one week, the epithelium and the equatorial parts of superficial lens fibers contain extracellular spaces. The extracellular spaces together with locally disarranged fibers produce a corrugated opaque lens surface and equatorial opacities. Within several weeks after ex

Animals↗

PubMed1993

Decreased erythrocyte Na+,K(+)-ATPase activity associated with cellular potassium loss in extremely low birth weight infants with nonoliguric hyperkalemia.

To determine whether a shift of potassium ions from the intracellular space to the extracellular space accounts, in part, for the hyperkalemia seen in extremely low birth weight infants, we examined potassium concentration in serum and erythrocytes from extremely low birth weight infants with hyperkalemia (n = 12) or with normokalemia (n = 27). In addition, to determine whether the shift of potassium was associated with low sodium-potassium-adenosinetriphosphatase (Na+,K(+)-ATPase) activity, we studied the activity of ATPase in the last 16 infants enrolled in the study. Fluid intake and output were measured during the first 3 days of life. Infants were considered to have hyperkalemia if the serum potassium concentration was 6.8 mmol/L or greater. Blood was obtained daily for intracellular sodium and potassium levels by means of lysis of erythrocytes. The remaining erythrocyte membranes were frozen and analyzed for Na+,K(+)-ATPase activity. There were significantly lower intracellular potassium/serum potassium ratios in the infants with hyperkalemia for each day of the 3-day study (p < 0.001). In the hyperkalemic group, there was lower Na+,K(+)-ATPase activity than in the infants with normokalemia (p = 0.006). Low Na+,K(+)-ATPase activity was associated with lower intracellular potassium/serum potassium ratios (p = 0.006), higher serum potassium values (p = 0.02), and lower intracellular potassium concentration (p = 0.009). The urinary data demonstrated that there was no difference in glomerulotubular balance between the two groups. We conclude that nonoliguric hyperkalemia in extremely low birth weight infants may be due, in part, to a shift of potassium from the intracellular space to the extracellular space associated with a decrease in Na+,K(+)-ATPase activity.

Bilirubin↗

PubMedDate not supplied

Extracellular (36Cl) space, electrolyte, protein, and DNA content in brain of DBA and C57 mice: effects of age.

DBA/2J (DBA) mice are susceptible to audiogenic seizures (AGSs) in an age-dependent manner, susceptibility being maximal at 21 days and absent at 110 days of age. Previous studies have demonstrated that there is a decrease in anion transport and an increase in carbonic anhydrase (CA) activity in brain from DBA mice as compared with C57BL/6J (C57, non-AGS) mice at 21 days. Since these results suggest that there are alterations in cellular and electrolyte composition of brain from DBA mice, the present work was directed toward determining electrolyte content, extracellular space, and DNA content of brain from DBA and C57 mice at 21 and 110 days of age. There was a decrease in intracellular chloride and sodium content, and an increase in intracellular potassium content in cerebral cortex, cerebellum, and brainstem from DBA mice at both 21 and 110 days. Also, extracellular space was larger in these three brain tissues from DBA mice at both ages. DNA content, not different between the strains at 21 days, was significantly lower in cerebellum from DBA mice at 110 days. These findings give further evidence of alterations in the transport of ions in brain from DBA mice. In addition, they demonstrate that there are alterations in the intracellular and extracellular space values, an indication of changes in cellular composition of brain in these mice. Such changes may contribute to AGS susceptibility by disrupting the balance that normally exists in the neuronal microenvironment of the central nervous system.

Acoustic Stimulation↗

PubMed1979

Ultrastructural evidence for remodelling in a central noradrenergic pathway following electrolytic lesioning.

Electrolytic lesions were carried out in the medial hypothalamus of adult rats to study remodelling responses in a central noradrenergic pathway, the medial forebrain bundle. Four days, two weeks, 4 weeks and 8 weeks post-lesion, the animals were perfused and processed for correlated fluorescence microscopic (FM) and electron microscopic (EM) study. FM evaluation 4 days post-lesion showed that, compared with control preparations, catecholaminergic fibers became thick, distorted and intensely fluorescent. With increasing survival times the caliber of these fibers became finer and fluorescence intensity was gradually diminished. Some of the small blood vessels in the vicinity of the lesion acquired an intense perivascular fluorescence. Electron microscopic examination of the lesion site 4 days post-lesion disclosed many degenerating axons and increased extracellular space. No increased extracellular space was discerned by 8 weeks post-lesion. After all survival periods greatly enlarged axonal profiles were seen, and these resembled 'growth cones' described in earlier tissue culture, developmental and peripheral nervous system studies.

Adrenergic Fibers↗

PubMed1996

Response of cell volume in Mytilus gill to acute salinity change.

The response of gill cell volume in Mytilus californianus and Mytilus trossolus (=edulis) to acute changes in salinity was assessed using three independent indicators: optical measurement of lateral cell height, measurement of intracellular water content using radiolabeled tracers and measurement of the contents of the major osmolytes of the gills. Optical measurements indicated significant variation in the response of individual lateral cells of M. californianus to acute low-salinity shock. Lateral cell height increased by approximately 20% shortly after abrupt exposure to 60% artificial sea water (ASW). Following this initial swelling, we estimate that a substantial regulatory volume decrease (RVD) was present in 25% of the trials. More commonly, however, an RVD was either absent or minimal: cell height remained elevated for at least 1 h, then returned to the control height when gills were re-exposed to 100% ASW. Changes in the combined water space of all cells in the gill, measured as the difference between total water space and extracellular space ([14C]polyethylene glycol space), indicated that cell volume regulation in the gill as an organ was also absent or minimal. Cell water space was 2.16 ml g-1 dry mass in isolated gills of M. californianus acclimated to 100% sea water in the laboratory and increased to 2.83 ml g-1 dry mass after a 6 min exposure to 60% ASW. Cell water space was still 2.81 ml g-1 dry mass after 1 h in 60% ASW and returned to 2.06 ml g-1 dry mass upon re-exposure to 100% ASW. Consistent with these observations, the gill contents of the principal cytoplasmic osmolytes (taurine, betaine and K+) were unchanged (approximately 450, 250 and 230 mu mol g-1 dry mass, respectively) following exposure of gills from 100% ASW-acclimated mussels to 60% ASW. A decrease in cell water space to 2.66 ml g-1 dry mass after 4 weeks of acclimation to 60% ASW corresponded with a 37% decrease in betaine content; taurine and K+ contents were unchanged. The changes in water space and solute content of gills from freshly collected M. californianus and M. trossolus were also consistent with the absence of volume regulation; cell water space remained elevated for at least 1 h after low-salinity exposure, and solute contents were unchanged after this period. We calculated the potential energetic cost of cell volume regulation for mussels exposed to 12 h of sinusoidal fluctuations between 100% and 50% sea water; solute uptake for full volume regulation in all tissues would cost a minimum of approximately 30% of the standard metabolic rate during the period of salinity increase. The routine absence of substantial cell volume regulation in Mytilus gill may reflect the potentially high energetic cost of volume regulation in the face of the large and frequent salinity fluctuations that are regularly encountered by estuarine bivalves.

Animals↗

PubMed1998

Determination of the intracellular sodium concentration in perfused mouse liver by 31P and 23Na magnetic resonance spectroscopy.

A combination of 31P and 23Na NMR spectroscopy has been used to quantify the concentration of intracellular sodium, [Na]IC in the isolated and perfused mouse liver. The 31P resonances of dimethyl methylphosphonate and LaDOTP5-, markers of total tissue space and extracellular space, respectively, were used to determine the intracellular liver volume. For a mean wet weight of 1.7 +/- 0.3 g, the intracellular liver volume as measured by 31P NMR averaged 1.2 +/- 0.2 ml. The amount of intracellular sodium was measured from the baseline-resolved intracellular 23Na resonance during perfusion of the shift reagent, TmDOTP5-. These two measurements resulted in an NMR-determined value for [Na]IC of 29.0 +/- 5.2 mM. Separate measurement of total tissue Tm and Na by atomic absorption spectroscopy on the same samples provided an AAS-determined value for [Na]IC of 32.1 +/- 7.4 mM. These results indicate that intracellular sodium in the isolated, perfused liver is 100% visible by 23Na NMR spectroscopy.

Animals↗

PubMed1995

Internal potassium shift in premature infants: cause of nonoliguric hyperkalemia.

To study the pathophysiology of nonoliguric hyperkalemia, we measured serum potassium concentration and external K balance (intake and excretion), and estimated internal K balance (a shift from intracellular space to extracellular space) in 24 nonoliguric premature infants during the first 72 hours after birth. Data were analyzed from two aspects: gestational age (group 1, 24 to 28 weeks, n = 9; group 2, 29 to 32 weeks, n = 9; group 3, 33 to 36 weeks, n = 6) and postnatal age (0 to 72 hours). Serum K concentration rose from baseline (0 hour) to 24 hours in groups 1 and 2 (p < 0.01) but did not rise in group 3. The external K balance was negative in all groups during the study period, and was more negative in the more premature infants (group 1 > group 2 > group 3) during the second 24 hours. There was a significant difference (p < 0.01) between the internal K balance of the three groups during the first 24 hours (group 1 > group 2 > group 3), and the K shift decreased significantly (p < 0.05) during the study period in groups 1 and 2. The more premature the infants, the larger the K shift and the larger the rise in serum K concentration during the first 24 hours, and the more negative the external K balance after 24 hours. These data indicate that K loading caused by the K shift associated with prematurity produces a rapid rise in serum K concentration, resulting in an increase in urinary K excretion. We conclude that an internal K shift inversely proportional to gestational and postnatal age is the primary cause of nonoliguric hyperkalemia in very premature infants.

Extracellular Space↗

PubMed1998

A novel 13C NMR method to assess intracellular glucose concentration in muscle, in vivo.

Intracellular glucose concentration in skeletal muscle of awake rats was determined under conditions of hyperglycemic (10.2 +/- 0.6 mM) hyperinsulinemia (approximately 1,200 pM) and hyperglycemic (20.8 +/- 1.5 mM) hypoinsulinemia (< 12 pM) by use of 13C nuclear magnetic resonance (NMR) spectroscopy during a prime-constant infusion of [1-13C]glucose and [1-13C]mannitol with either insulin (10 mU.kg-1.min-1) or somatostatin (1.0 microgram.kg-1.min-1). Intracellular glucose was calculated as the difference between the concentrations of total tissue glucose (calculated from the in vivo 13C NMR spectrum with mannitol as an internal concentration standard) and extracellular glucose, corrected by the ratio of intra- and extracellular water space. Extracellular concentration was corrected for an interstitial fluid-to-plasma glucose concentration gradient of 0.83 +/- 0.07, determined by open-flow microperfusion. The mean ratio of intra- to extracellular glucose space, determined from the relative NMR signal intensities and concentrations of mannitol and total creatine, was 9.2 +/- 1.1 (hyperglycemic hyperinsulinemia, n = 10), and 9.0 +/- 1.7 (hyperglycemic hypoinsulinemia, n = 7). Mean muscle intracellular glucose concentration was < 0.07 mM under hyperglycemic-hyperinsulinemic conditions (n = 10) and 0.32 +/- 0.06 mM under hyperglycemic-hypoinsulinemic conditions (n = 7). This method is noninvasive and should prove useful for resolving the question of whether glucose transport or phosphorylation is responsible for the reduced rate of muscle glycogen synthesis observed in diabetic subjects.

Animals↗

PubMed1980

Role of the interstitial matrix during intestinal volume absorption.

The effects of net volume absorption rate (Jv,m) on intestinal interstitial fluid volume (VI), lymph flow (JL), and the excluded volume fraction for interstitial albumin (FE) were analyzed in an autoperfused cat ileum preparation. Tissue blood volume, extracellular space, and extracellular albumin (VA) were estimated using 51Cr-labeled red blood cells, 99mTc-labeled diethylenetriamine pentaacetic acid (DTPA), and 125I-labeled human serum albumin, respectively. Nonabsorptive values of 27.8 ml/100 g, 18.2 ml/100 g, and 0.37 were acquired for VI, VA, and FE, respectively. Net volume absorption results in an increase in intestinal interstitial volume and lymph flow and decreases the degree of albumin exclusion in the interstitial matrix. The magnitude of the changes in interstitial volume, lymph flow, and excluded volume of albumin during net volume absorption are related to the rate of absorption. The increased matrix hydration during absorption serves to enchance vascular and lymphatic removal of absorbed volume.

Animals↗

PubMed1999

Distribution and space-time relationship of proteoglycans in the extracellular matrix of the migratory pathway of primordial germ cells in mouse embryos.

In this paper we present an in situ ultrastructural cytochemical study on the distribution and spatial-temporal expression of proteoglycans (PGs) in the extracellular matrix of the migratory pathway of mouse primordial germ cells (PGCs) during the different phases of migration, by the use of the cationic dye ruthenium hexammine trichloride (RHT). Embryos of 9, 10, 11 and 12 days of development were used. The treatment with RHT revealed PGs as electron dense layers, granules, and filaments. Whereas granules prevailed in the extracellular spaces of the migratory route during the whole migratory process, the amount of filamentous structures increased during the migration phase of PGCs. At the end of the migratory process the surface of the PGCs lost its reaction by RHT. There were differences in the size of the granules of PGs at the initial migratory period (9-day-old embryos) as compared with the other days of gestation. There was a strong reaction for PGs in the extracellular spaces, expressed as a meshwork of granules interconnected by filaments, as well as reaction on the basement membranes during the peak of the PGCs migration in 10-day-old embryos. These results support the hypothesis that these molecules may have an important role in the migration of PGCs, although the precise mechanism involved in this process is not yet clear.

Animals↗

PubMed1991

Collagen fibril assembly and deposition in the developing dermis: segmental deposition in extracellular compartments.

The hierarchy of extracytoplasmic compartmentalization and fibrillar organization as well as the assembly and deposition of collagen fibrils was characterized in the 15-day chick embryo dermis using transmission electron microscopy. At least two levels of extracellular compartmentalization are recognizable at this stage of dermal development. The first compartment consists of a series of narrow channels containing single or small groups (less than 5) of collagen fibrils. These channels course deep within the cell and are open to the extracellular space. The second extracellular compartment consists of fibrils grouped as small bundles in close association with the cell surface and is most often defined by a single fibroblast. A third level of fibril organization and compartmentalization is sometimes apparent at this stage of dermal development consisting of laterally associated bundles, more characteristic of the mature dermis. This compartment is associated with the fibroblast surface, but is less well defined than the fibril channels or bundle-forming compartments. Dermal collagen fibrils within bundles are discontinuous. Numerous fibrils ends are identified from serial sections and the ends gradually taper. These data indicate that the dermal fibroblast compartmentalizes the extracellular space and deposits collagen fibril segments during dermal morphogenesis. A model for the genesis of the extracellular compartments and their role in collagen fibrillogenesis and development of regularly arranged connective tissues, tendon, and cornea has been proposed. Dermal development conforms to this model and we suggest that extracytoplasmic compartmentalization of the steps in matrix assembly and segmental deposition of collagen fibrils are important mechanisms in the development of a wide variety of connective tissues.

Animals↗

PubMed2001

TmDOTP(5-) as a (23)Na shift reagent for the subcutaneously implanted 9L gliosarcoma in rats.

The use of TmDOTP(5-) as an in vivo (23)Na NMR shift reagent (SR) for subcutaneously implanted 9L gliosarcoma was evaluated. TmDOTP(5-) produced a single sharp extracellular peak after about 50-60 min of infusion, and did not cause any changes in the (31)P resonance areas or chemical shifts, suggesting that the SR is homogeneously distributed in the extracellular space and does not alter tumor bioenergetic status. TmDOTP(5-) and CoEDTA(-) as extracellular space markers gave identical results for relative extracellular space (0.25 +/- 0.03 and 0.25 +/- 0.04, respectively) and intracellular Na(+) concentration (19.3 +/- 4.0 mM and 18.6 +/- 3.9 mM, respectively), indicating that the biodistribution of the SR is the same as the well-accepted extracellular space marker. The in vivo T(1) and T(2) relaxation times of intra- and extracellular Na(+) were also measured. Our results indicate that TmDOTP(5-) promises to be an effective shift reagent and extracellular space marker in the 9L gliosarcoma and perhaps other tumors. Magn Reson Med 45:436-442, 2001.

Animals↗

PubMed2003

A mathematical study of volume shifts and ionic concentration changes during ischemia and hypoxia.

The response of tissue to ischemia (cessation of blood flow and deprivation of oxygen) includes swelling of the intracellular space, shrinkage of the extracellular space, and an increase in the extracellular potassium concentration. The responses of cardiac and brain tissue to ischemia are qualitatively different in that cardiac tissue shows a rise in extracellular potassium over several minutes from about 5 to 10-12 mM followed by a plateau, while brain tissue shows a similar initial rise followed by a very rapid increase in extracellular potassium to levels of 50-80 mM. During hypoxia the flow of blood (or perfusate) is maintained and, while there is a substantial efflux of potassium from cells, there is little accumulation of potassium in the interstitium. A mathematical model is proposed and studied to try to elucidate the mechanism(s) underlying the increase in extracellular potassium, and the different time courses seen in neural and cardiac tissue. The model involves a Hodgkin-Huxley-type description of transmembrane ion currents, allows for ion concentrations as well as volumes to change for both the intracellular and extracellular space, and includes coupling of damaged tissue to nearby healthy tissue. The model produces a response to ischemia much like that seen in neural tissue, and the mechanism underlying this response in the model is determined. The same mechanism is not present in cardiac ion models, and this may explain the qualitative difference in response shown in cardiac tissue.

Animals↗

PubMed1988

A role for Ca2+ in mediating hormone-induced biphasic pepsinogen secretion from the chief cell determined by luminescent and fluorescent probes and X-ray microprobe.

In isolated chief cells from the guinea pig, cholecystokinin (10 nM) and a high concentration of ionomycin each caused a biphasic pattern of pepsinogen secretion. The initial fast response to cholecystokinin was not dependent on medium Ca2+ ans was mimicked by low concentration of ionomycin (100 nM). Inositol 1,4,5-trisphosphate caused a similar fast release from permeabilized cells. The slow component of release was dependent on medium Ca2+, however, and was mimicked by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) (100 nM) or the diacylglycerol analogue 1-oleoyl-2-acetylglycerol (OAG) (100 microM). Ionomycin (100 nM) and TPA (and/or OAG), when applied together, reproduced the biphasic pattern of pepsinogen secretion, suggesting that the signalling pathways utilized by both types of agonist contribute to the response evoked by cholecystokinin-hormone stimulation. Both fura-2 and aequorin were used to monitor changes of intracellular Ca2+. Three pathways were found to contribute to the Ca2+ transient. A rapid release of Ca2+ from intracellular store(s), a rapid Ca2+ entry from the extracellular space, and a more sustained Ca2+ entry from the extracellular space. Cholecystokinin induced a rapid increase in cytoplasmic Ca2+ ([Ca2+]i) as estimated with fura-2 and aequorin. This rise was reduced but not abolished upon removal of extracellular Ca2+, suggesting that both Ca2+ entry from the extracellular space and Ca2+ mobilization from the intracellular store(s) contribute to the initial, fast component of the Ca2+ transient. A second, more sustained component of the Ca2+ transient induced by cholecystokinin was abolished by lanthanum. TPA and OAG induced a biphasic Ca2+ transient that could be detected only with aequorin. The late, sustained component of this response was again abolished by lanthanum as well as by removal of extracellular Ca2+. It appears that the late component of the Ca2+ transient is dependent on Ca2+ influx from the extracellular space and is too localized to be detected by fura-2. Prestimulation of cells with TPA or OAG prevented the aequorin transient caused by cholecystokinin and vice versa, suggesting that TPA, OAG and cholecystokinin activate the same pathways of Ca2+ entry into the cytosol from the intracellular store(s) or the extracellular space. The stimulation-sensitive Ca2+ pool was examined with electron probe X-ray microanalysis. It appears to be restricted to an area enriched in secretory granules or peripheral endoplasmic reticulum just beneath the apical plasma membrane and in close association with the microtubular-microfilamentous system.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

Trans-sarcolemmal Ca2+ movements associated with contraction of the rabbit right ventricular wall.

The purpose of this study was to examine the movements of Ca2+ into the myocardium from the extracellular space during the course of muscle contraction. Equilibration of the rabbit right ventricular wall with perfusate containing 45Ca was measured by collecting effluent droplets over time. This protocol was carried out in a quiescent muscle and then repeated 15-20 minutes later in an identical fashion except that halfway through the collection period the muscle was stimulated to contract. We were thus able to quantitate the contraction-dependent changes in 45Ca movements. In control experiments using [58Co]EDTA as an extracellular space marker, we observed that contraction altered the volume of this space. This alteration in extracellular space was relatively small, and the quantitation of 45Ca movements was corrected for this change. The addition of 1 microM Bay K 8644 to the perfusate stimulated tension and augmented Ca2+ depletion from the extracellular space. The addition of 15 microM nifedipine to the perfusate significantly reduced both tension development and Ca2+ depletion from the extracellular space of the muscle. Net contraction-dependent movement of Ca2+ from the extracellular space into the myocardium under control conditions at 1 mM [Ca2+] was 10-14 mumol Ca2+/kg tissue wet wt/beat. This value indicates either a large contribution of Ca2+-induced Ca2+ release from the sarcoplasmic reticulum and/or significant contribution of sarcolemmal bound Ca2+ to excitation-contraction coupling in the rabbit ventricle.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1971

A new approach for determining the volume of cerebral cellular fluid and demonstration of its communication with C.S.F.

1. A new technique is presented for determining the volume of extracellular space in bowfin (Amia calva) brain during in vitro incubation. It consists of solving simultaneous equations which are applied to determine the volume of extracellular space as well as intracellular marker concentration. This technique allows for a better insight into the redistribution of marker between incubation medium and extracellular space as well as between extracellular and intracellular space.2. Na(+), K(+) and Cl(-) equilibrated within 10-15 min between incubation medium and extracellular space. There was no evidence of a homoeostatic mechanism controlling the concentration of these ions in the extracellular fluid, which appeared to be in equilibrium with cerebrospinal fluid. The extracellular spaces of these ions were identical: Na(+), 23.4; K(+), 23.3 and Cl(-), 23.2%.3. Sorbitol equilibrated with the extracellular fluid within 45 min and indicated an extracellular space of 22.6%, nearly identical with that for electrolytes.4. Vastly different ;spaces' were obtained for [(3)H]methoxy inulin, which equilibrated within 45 min with a 13% space and [(14)C]carboxyl inulin, which showed a 46% space value for only 30 min. The difference may be explained by marker decomposition. The 9% difference between the [(3)H]methoxy inulin and sorbitol spaces may be explained by a ;packing' factor attributable to molecular size.

Animals↗

PubMed2002

Molecular identification of P-glycoprotein: a role in lens circulation?

PURPOSE: To determine whether P-glycoprotein is expressed in the rat lens and to assess what type of damage occurs when P-glycoprotein inhibitors are applied to organ-cultured lenses. METHODS: An initial screening for the P-glycoprotein isoforms multidrug resistance (mdr)1a, mdr1b, and mdr2 was performed by RT-PCR on RNA extracted from rat lens fiber cells. Northern blot analysis was used to determine whether transcript levels detected by RT-PCR were significant. The presence of P-glycoprotein in the lens was confirmed by Western blot analysis and immunocytochemistry. Organ-cultured lenses, maintained in isotonic artificial aqueous humor, were exposed to various concentrations of the P-glycoprotein inhibitor tamoxifen. Lens opacification was assessed by dark-field microscopy, and the underlying cellular changes were visualized by confocal microscopy of lens sections, using a fluorescent membrane marker. Initial cellular damage was assessed after a 6-hour exposure to 100 micro M tamoxifen. Other P-glycoprotein inhibitors, verapamil, and 1,9-dideoxyforskolin (DDFK) were assessed, and the damage phenotypes were compared with those seen for tamoxifen. RESULTS: Transcript for all three P-glycoprotein isoforms was detected with RT-PCR, but only mdr1a and mdr2 could be detected by Northern blot analysis. P-glycoprotein was localized in the plasma membrane of lens epithelial and fiber cells. Treatment of organ-cultured lenses with increasing doses of the P-glycoprotein inhibitor tamoxifen for 18 hours showed that two distinct damage phenotypes were evident. At a dose of 20 micro M tamoxifen, tissue damage was found in a discrete zone that initially started approximately 100 micro m from the capsule, whereas at higher doses (60-100 micro M tamoxifen), extensive vesiculation of fiber cell membranes occurred throughout the entire lens cortex. Decreasing tamoxifen (100 micro M) exposure to 6 hours showed that the inner zone of damage was caused by the dilation of extracellular space between fiber cells. The extracellular space dilution and fiber cell vesiculation could be reproduced by varying the concentrations of other P-glycoprotein inhibitors, verapamil and DDKF. CONCLUSIONS: The P-glycoproteins mdr1a and mdr2 are expressed in the lens and appear to be functional. The initial cellular damage phenotype of extracellular space dilations caused by the P-glycoprotein inhibitors was identical with that caused by chloride channel inhibitors, indicating that P-glycoprotein may play a role in regulating cell volume in the lens. Whether the secondary damage phenotype of fiber cell vesiculation, induced by high doses of P-glycoprotein inhibitors, was due to the inhibition of additional regulatory activities of P-glycoprotein or to nonspecific effects of the drugs remains to be determined. However, regardless of the precise mode of action, these results indicate that P-glycoprotein should be considered in the regulatory mechanisms associated with the control of lens volume and in the initiation of osmotic cataract.

ATP Binding Cassette Transporter, Subfamily B↗