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C Crone

Publications and source records attributed to C Crone.

At least 55 records · Page 3Linked to original sources
PubMed1986

Terminology for mass transport and exchange.

Virtually all fields of physiological research now encompass various aspects of solute transport by convection, diffusion, and permeation across membranes. Accordingly, this set of terms, symbols, definitions, and units is proposed as a means of clear communication among workers in the physiological, engineering, and physical sciences. The goal is to provide a setting for quantitative descriptions of physiological transport phenomena.

Animals↗
PubMed1986

Modulation of solute permeability in microvascular endothelium.

Modulation of macromolecular permeability involves creation of venular leaks in response to receptor-operated mechanisms in the endothelial cell membrane elicited by various autacoids (histamine, serotonin, bradykinin). Reversible modulations may occur within seconds in response to specific agents, which indicates receptor-mediated events that act via the endothelial cells' contractile apparatus, leading to subtle changes in junctional microtopography and allowing faster passage of small solutes. This mechanism probably involves activation of the actin-myosin system in endothelial cells. Ca2+ is an important signal substance, as reflected in the permeability-increasing effect of calcium ionophores. The junctional control system may share functional similarities with the contractile system in various types of muscle cells, in particular, smooth muscle. This suggests a function for the extensive vesicular invaginations of the plasmalemmal membrane present in endothelial cells. Rather than being a system to carry macromolecules across the endothelium, its physiological role may be to regulate free cytosolic calcium concentration. It is reminiscent of similar membrane invaginations found in muscle cells. Thus intracellular free calcium may be regulated by a combination of energy-requiring extrusion and passive influx through receptor-operated calcium channels located in the invaginated vesicular membranes, with short diffusion distances to the actin-myosin filaments in the cytoplasm.

Animals↗
PubMed1985

Reciprocal Ia inhibition from the peroneal nerve to soleus motoneurones with special reference to the size of the test reflex.

The aim of the study was to examine the supraspinal control during voluntary movements of the foot in man, of the Ia inhibitory interneurones activated from the anterior tibial muscle and projecting to the soleus alpha-motoneurones. Previous studies have reported an increased inhibition of the soleus alpha-motoneurones by a constant conditioning stimulus to the common peroneal nerve during dorsiflexion of the foot. This was interpreted as a sign of supraspinal facilitation of the Ia inhibitory interneurones. However, these results could not be reproduced in the present study. The contradictory results can probably be explained by some important methodological differences in the use of the H-reflex technique.

Adult↗
PubMed1985

Permeability of single capillaries.

The development and use of electrophysiological methods in the study of the permeability of single capillaries are described. On the whole, the values obtained with single vessels correspond satisfactorily to those obtained from whole organs by use of tracer techniques. The findings support the contention that whole organ techniques allow assessment of capillary permeability with a reasonable accuracy. There is a large range of small solute permeabilities among different 'continuous' capillaries spanning from 7 x 10(-4) cm sec-1 in the mesentery to 3 x 10(-7) cm sec-1 in the brain. The finding of different permeabilities between capillaries in various organs can be rationalised in terms of the pore theory. Thus the results comply with a physical membrane having pore densities ranging from 10 per micron2 (mesentery) to 0.01 per micron2 (brain). Since-in all likelihood-ion permeation primarily takes place via the junctional zones between endothelial cells these differences probably refer to subtle differences in the nature and complexity of junctional contacts.

Animals↗
PubMed1984

Lack of selectivity to small ions in paracellular pathways in cerebral and muscle capillaries of the frog.

Selectivity to passive permeation of small ions through capillary walls was studied by measurements of diffusion potentials in response to ionic gradients established across capillary walls in frog brain and muscle in superfusion and perfusion experiments. Average dilution potentials in response to 2:1 or 10:1 gradients of NaCl across brain capillaries were 4.2 and 10.2 mV, respectively. The 'diluted' side was negative with respect to the 'undiluted' side, reflecting higher mobility of Cl- than of Na+ ions. Bi-ionic potentials in response to isosmotic KCl:NaCl gradients averaged 5.0 mV in brain capillaries, negative on the KCl side, reflecting higher mobility of K+ than of Na+ ions. The potential variations were symmetrical across the capillary wall. From Planck-Henderson formalism, the relative permeabilities in brain capillaries of Na+, K+ and Cl- were PCl/PNa:1.54 and PK/PNa:1.56, rather close to mobility ratios in free solution. Experiments on muscle capillaries showed similar results to those in brain. Streaming potentials created with excess (200 mosmol) mannitol or sucrose were congruent to 1 mV in brain capillaries and zero in muscle capillaries. It is concluded that the transcapillary permeation pathway in muscle and brain is neutral or weakly charged. The dominant ion permeation is paracellular in all 'continuous' capillaries. The large range of ion permeability of 'continuous' capillaries may be explained by variation in the length of the effective open portion of interendothelial junctions. The very low passive permeability of the blood-brain barrier may be due to an almost closed endothelial junction, leaving only about 0.1% of the length open. The open fraction is functionally similar to that in muscle and mesentery. This interpretation is in accordance with a finite, but very low, permeability to hydrophilic non-electrolytes. Such a brain capillary would still display strong preference for lipid-soluble solutes, but its behaviour cannot be satisfactorily understood from a simple analogy to a cellular plasma membrane.

Amiloride↗
PubMed1983

Biochemical modulation of blood-brain barrier permeability.

Hydrophilic substrates necessary for brain function cross the capillary by facilitated diffusion. The facilitation has many features in common with enzyme-catalyzed reactions and is probably subserved by protein entities in the endothelial wall. The proteins act as receptors, recognizing substrate molecules, and as translocators, giving the molecules access to an aqueous path through the endothelium. These receptor-translocators can be saturated, and the transport is subject to competitive inhibition by substrate analogs. Thus, amino acids inhibit the transport of each other, and galactose can inhibit glucose transport in suckling rats. The proteins can be induced, as in the case of ketone transport in starvation, and repressed, as in the case of glucose transport in hyperglycemia. In rats with hyperglycemia for three weeks, the maximum glucose transport capacity of the blood-brain barrier decreased from 400 to 290 mumol/hg/min. An important result of the description is the understanding that rigid distinctions between the function of receptors, translocators, and enzymes is impossible. Understanding of the biochemical properties of facilitated diffusion may help explain a variety of symptoms in many 'inborn errors of metabolism'. This understanding has followed greater, recent insights into the general properties of the blood-brain barrier (45,46,47).

Adaptation, Physiological↗
PubMed1983

The three-dimensional organization of plasmalemmal vesicular profiles in the endothelium of rat heart capillaries.

The organization of plasmalemmal vesicular profiles in the endothelium of rat heart capillaries has been reinvestigated. Judged from random thin sections approximately 50% of the vesicles appeared free in the cytoplasm, the rest opening to the surfaces of the endothelial cells--a distribution which corroborates previous studies. However, three-dimensional reconstructions based on ultrathin serial sections (thickness congruent to 12 nm) gave a very different picture. All plasmalemmal vesicular profiles (921 from 5 capillaries) were parts of the surface membrane either as caveolae or as more complex racemose invaginations. This organization has previously been observed in frog mesenteric capillaries ((M. Bundgaard, J. Frøkjaer-Jensen, and C. Crone, 1979, Proc. Nat. Acad. Sci. USA 76, 6439-6442) and (J. Frøkjaer-Jensen, 1980, J. Ultrastruct. Res. 73, 9-20)). It is therefore proposed that absence or extreme rarity of free plasmalemmal vesicles is a general feature of capillary endothelia. Consequently, we suggest that the term "endothelial, plasmalemmal vesicles" be replaced by "endothelial plasmalemmal invaginations." The results imply that trans-endothelial vesicular transport is unlikely to occur and that this membrane system performs other--as yet unknown--functions.

Animals↗
PubMed1983

Electrical resistance of muscle capillary endothelium.

A recently developed technique for in vivo determination of the electrical resistance of vascular endothelium in microvessels was applied to the vessels in a thin frog muscle, m. cutaneus pectoris. The technique consists of injection of current via a glass micropipette into a capillary and measurement of the resulting intra- and extravascular potential profiles with another micropipette placed at various distances from the current source. The theory of Peskoff and Eisenberg (1974) was used to handle the problems arising from distributed extravascular resistances and was experimentally shown to describe the external field satisfactorily. With this extension of one-dimensional cable theory the specific electrical resistance of arterial microvessels was 33 omega cm2 and of venous capillaries 23 omega cm2. The "length constants" were 135 and 112 micrometers, respectively. If results from arterial and venous vessels are taken together, the ionic permeabilities at 20 degrees C were PNa = 3.9 X 10(-5) cm X s-1, PK = 5.7 X 10(-5) cm X s-1, PCl = 5.9 X 10(-5) cm X s-1 and PHCO3 = 3.4 X 10(-5) cm X s-1. These figures agree with figures for capillary permeability obtained in tracer experiments on whole muscle. The study bridges a gap between single capillary and whole organ techniques with the conclusion that the two different approaches lead to similar results in muscle capillaries.

Animals↗
PubMed1982

Electrical resistance of brain microvascular endothelium.

A newly developed technique for determination of the electrical resistance of the capillary wall was applied to microvessels at the surface of the frog brain. Current was injected into a capillary or venule via a microelectrode and the ensuing intravascular potential profile away from the current source was determined with a second microelectrode placed at various positions along the capillary. The membrane resistance was calculated according to the theory for leaky cables used in determinations of axon membrane resistance. The average resistance was 1870 omega . cm2. Since the surface vessels of the frog brain are devoid of glial investment but otherwise similar to brain parenchymal vessels, the results prove that the endothelium is the site of the blood-brain barrier. The electrical resistance is similar to that of a 'tight' epithelium.

Animals↗
PubMed1981

Blood-brain glucose transfer: repression in chronic hyperglycemia.

Diabetic patients with increased plasma glucose concentrations may develop cerebral symptoms of hypoglycemia when their plasma glucose is rapidly lowered to normal concentrations. The symptoms may indicate insufficient transport of glucose from blood to brain. In rats with chronic hyperglycemia the maximum glucose transport capacity of the blood-brain barrier decreased from 400 to 290 micromoles per 100 grams per minute. When plasma glucose was lowered to normal values, the glucose transport rate into brain was 20 percent below normal. This suggests that repressive changes of the glucose transport mechanism occur in brain endothelial cells in response to increased plasma glucose.

Animals↗
PubMed1981

Electrical resistance of a capillary endothelium.

The electrical resistance of consecutive segments of capillaries has been determined by a method in which the microvessels were treated as a leaky, infinite cable. A two-dimensional analytical model to describe the potential field in response to intracapillary current injection was formulated. The model allowed determination of the electrical resistance from four sets of data: the capillary radius, the capillary length constant, the length constant in the mesentery perpendicular to the capillary, and the relative potential drop across the capillary wall. Of particular importance were the mesothelial membranes covering the mesenteric capillaries with resistances several times higher than that of the capillary endothelium. 27 frog mesenteric capillaries were characterized. The average resistance of the endothelium was 1.85 omega cm2, which compares well with earlier determinations of the ionic permeability of such capillaries. However, heterogeneity with respect to resistance was observed, that of 10 arterial capillaries being 3.0 omega cm2 as compared with 0.95 omega cm2 for 17 mid- and venous capillaries. The average in situ length constant was 99 micrometers for the arterial capillaries and 57 micrometers for the mid- and venous capillaries. It is likely that the ions that carry the current must move paracellularly, through junctions that are leaky to small solutes.

Animals↗
PubMed1979

Endothelial plasmalemmal vesicles as elements in a system of branching invaginations from the cell surface.

In electron microscopy studies of the endothelial vesicles in frog mesenteric capillaries, an accidental observation was made concerning vesicular organization. When tannic acid was added to already fixed tissue, the mordant reached apparently free vesicles in the cytoplasm under conditions in which vesicular movement was excluded and in which the impermeability of the cell membranes was preserved. This indicates a spatial continuity between the vesicles and the cell exterior. It is proposed that cytoplasmic vesicles in endothelial cells are elements of branching, permanent or semipermanent invaginations of the plasmalemma.

Animals↗
PubMed1979

Permeability of single capillaries compared with results from whole-organ studies.

There are now two experimental approaches to capillary permeability: whole-organ studies and single-capillary experiments. It is not possible to obtain permeability coefficients in the true sense of the word from whole-organ experiments since the capillary surface area is unknown. Other limitations of whole-organ approaches are discussed. Results from 'osmotic transient' experiments are compared with those from 'indicator diffusion' experiments. 'Osmotic transient' experiments give higher values for capillary diffusion capacity than 'indicator diffusion' experiments. Reasonable agreement is obtained when the reflection coefficient is taken into account. Thus far, single-capillary experiments have only provided results from capillaries in the frog mesentery, where the potassium permeability was about 70 X 10(-5) cm . sec-1, or 10 times the value from whole-organ experiments on muscle. The discrepancy may reflect true differences between capillaries in the two tissues or may be caused by methodological limitations. There is a need for comparative studies of permeability with the whole-organ and the single-capillary technique applied to the same tissue.

Animals↗