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Biomedical subjects

J Graf

Publications and source records attributed to J Graf.

At least 19 recordsLinked to original sources
PubMed1992

Relationship of hepatic cholate transport to regulation of intracellular pH and potassium.

Modulation of hepatic cholate transport by transmembrane pH-gradients and during interferences with the homeostatic regulation of intracellular pH and K+ was studied in the isolated perfused rat liver. Within the concentration range studied uptake into the liver was saturable and appeared to be associated with release of OH- and uptake of K+. Perfusate acidification ineffectually stimulated uptake. Application of NH4Cl caused intracellular alkalinization, release of K+ and stimulation of cholate uptake, withdrawal of NH4Cl resulted in intracellular acidification, regain of K+ and inhibition of cholate uptake. Inhibition of Na+/H(+)-exchange with amiloride reduced basal release of acid equivalents into the perfusate, initiated K(+)-release, and inhibited both, control cholate uptake and its recovery following intracellular acidification. K(+)-free perfusion caused K(+)-release and inhibited cholate uptake. K(+)-readmission resulted in brisk K(+)-uptake and recovery of cholate transport. Both effects were inhibited by amiloride. Interference with cholate transport through modulation of pH homeostasis by diisothiocyanostilbenedisulfonate (DIDS) could not be demonstrated because DIDS affected bile acid transport directly. Biliary bile acid secretion was stimulated by intracellular alkalinization and by activation of K(+)-transport. Uncoupling of the mutual interference between pH-dependent cholate uptake and K(+)-transport by amiloride indicates tertiary active transport of cholate. In this, Na+/K(+)-ATPase provides the transmembrane Na(+)-gradient to sustain Na+/H(+)-exchange which maintains the transmembrane pH-gradient and thus supports cholate uptake. Effects of canalicular bile acid secretion are consistent with a saturable, electrogenic transport.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

The blood supply of the Achilles tendon.

We have used a new technique of epoxy resin injection to examine the blood supply of the Achilles tendon. The posterior distal part showed poor vascularisation, as did the middle part of the tendon. Ruptures occur in the middle part, but only rarely in the distal part. We therefore suggest that there is no direct relationship between blood supply and the frequency of rupture.

Achilles Tendon↗
PubMed1992

[Importance of the subchondral space for development of chondromalacia patellae--morphologic study of joint cartilage of the rabbit patella after experimental ischemia].

The aetiology of chondromalacia patellae and especially the importance of the subchondral space have not been clarified to date. However, clinical findings yielded pointers to a connection between degenerative changes of the articular cartilage and an influence exercised by the subchondral space. In our experiments we performed an operative ischaemia of the patella with interruption of the vascular inflow and outflow on 40 adult rabbits for exactly defined times (2 weeks, 6 weeks, 3 months, 6 months). The examinations were carried out using the plastination method, histology, transmission electron microscopy, and scanning electron microscopy. Marked changes can be seen from the third month onwards: disappearance of the tidemark, degeneration of the cartilaginous cells (formation of clusters) and onset of trachomatous keratitis. These degenerative changes progress further in the animals of 6 months of age. The results indicate that metaplasia of the tidemark plays a significant part in the pathogenesis of degenerative changes of the cartilage. Hence, chondromalacia patellae can be caused by subchondral vascularisation disorders.--This is, therefore, a new concept for the aetiopathogenesis of chondromalacia patellae, a disease pattern that is of great importance in sports orthopaedics.

Animals↗
PubMed1992

Regulatory volume decrease stimulates bile flow, bile acid excretion, and exocytosis in isolated perfused rat liver.

To study the effect of volume regulation on bile secretory function, isolated perfused rat livers (IPRL) were exposed to hypotonic stress (45 mM NaCl) while bile flow and the biliary excretion of bile acids and horseradish peroxidase (HRP) were assessed. Hypotonic stress induced a biphasic increase in bile flow, which rose in the first minute from 1.1 +/- 0.2 to 1.7 +/- 0.1 microliter.min-1.g liver-1 (P less than 0.01), an effect attributed to rapid osmotic equilibration of water, then increased further between 3 and 5 min to 1.6 +/- 0.1 microliter.min-1.g liver-1 (P less than 0.01, followed by a subsequent return to baseline. HRP excretion in bile increased during the second peak of bile flow from 0.9 +/- 0.2 to 1.1 +/- 0.2 ng.min-1.g liver-1, P less than 0.01. Pretreatment with colchicine but not lumicolchicine completely abolished the latter increase in bile flow and HRP excretion as did BaCl2 (1 mM), an inhibitor of both K+ channels and regulatory volume decrease (RVD) in hepatocytes. When sodium taurocholate was infused (1 mumol/min), hypotonic stress induced an even larger increase in the second peak of bile flow (5.1 +/- 0.7 microliters/g liver, P less than 0.01) and higher rates of bile acid excretion than in control perfusions with bile acid (126.2 +/- 21.0 vs. 99.0 +/- 17.1 nmol.min-1.g liver-1, P less than 0.05). These data suggest that both bile flow and bile acid excretion are stimulated during RVD by mechanisms that involve both K+ channels and microtubule-dependent exocytosis at the canalicular (apical) membrane domain.

Animals↗
PubMed1992

Anion channels in rat liver canalicular plasma membranes reconstituted into planar lipid bilayers.

Previous studies from this laboratory have demonstrated a Cl(-)-HCO3- exchanger and have provided evidence for a Cl- conductance in rat liver canalicular plasma membrane vesicles. To further investigate the apical Cl- conductance, we performed single-channel analysis after incorporation of canalicular liver plasma membrane vesicles into planar lipid bilayers. This was necessary, because the canalicular membrane is not accessible for the patch-clamp technique. Two types of anion channels could be identified (30- and 90-pS conductance) corresponding to the class of small and intermediate channels, respectively. The kinetics of the small channel were found to be voltage dependent with a maximum for the open probability at -20 mV. In contrast, intermediate channel kinetics were voltage independent. The anion channels described above could allow electrogenic Cl- efflux, to compensate Cl- influx via the electroneutral Cl(-)-HCO3- exchanger. Further studies will be required to prove their functional importance in bile formation.

Animals↗
PubMed1992

Subchondral vascularisation and osteoarthritis.

A prospective experiment was carried out in 40 rabbits in which the blood supply to the patella was interrupted for defined periods from 2 weeks to 6 months. With prolonged ischaemia, there were clear changes in the articular cartilage which were comparable with those seen in human osteoarthritis.

Animals↗
PubMed1992

[What is the effect of para-articular fractures on hyaline joint cartilage? Experimental electron optic studies of the rabbit on post-traumatic subchondral vascularization disorders].

Joint fractures can interrupt the arterial and venous blood supply to the hyaline cartilage. Previous studies revealed effects of venous engorgement and hypertension in the cartilage. In this study the influence of interruption of the blood supply on the development of osteoarthritis was analysed. In a prospective, experimental study in 40 rabbits all vessels in the patella were ligated and the cartilage was investigated after 2, 6, 12, and 24 weeks by transmission electron microscopy. After 2 weeks no degenerative signs were determined. After 6 weeks there were distinct signs of cartilage injury. The degeneration of the hyaline cartilage increased with time. The endpoint of injury was the destruction of the cartilage and necrosis of the chondrocytes, determined after an ischaemic period of 24 weeks. The stages of cartilage degeneration in our trial correspond to the changes that are well known to occur in osteoarthritis. In conclusion, interruption of the blood supply of the patella results in degenerative changes to the joint cartilage. This effects is related to the duration of ischaemia. On the basis of results we recommend early and watertight repositioning of fractured joints not only for biomechanical reasons but also to avoid irrevocable effects of interrupted blood supply on hyaline joint cartilage.

Animals↗
PubMed1991

Fiber-optic measurement of intracellular pH in intact rat liver using pH-sensitive dyes.

The pH-sensitive fluorescent dye 1,3-dihydroxy-pyrene-6,8-disulfonic acid (DHPDS) was used to measure intracellular pH (pHi) from the surface fluorescence of the isolated perfused rat liver. Monochromatic light from a fluorometer was focused on the liver with a fiber optic, emitted light was collected with a second fiber bundle and returned to the spectrometer. To correct for changes in intracellular dye concentration, the excitation wavelength was changed between the pH-sensitive excitation peak wavelength and the isosbestic wavelength, then a ratio was computed between fluorescence intensities at these two wavelengths. Intracellular calibration of the dye was performed by clamping the intracellular to the extracellular pH with H+/K(+)-ionophore Nigericin. This method was used to monitor transient changes in intracellular pH caused either by addition and removal of NH4Cl or by changing perfusate CO2 and HCO3- concentrations while keeping their ratio constant. The effects of these maneuvers on bileflow were studied, too. Data obtained in the perfused liver were in good agreement with those obtained in isolated liver cells except that the steady-state pHi (7.46 +/- 0.02) was slightly higher than reported values. Measurements in livers of mutant TR- rats that are defective of dye secretion revealed similar pHi values, indicating that secretion of the dye into bile canaliculi did not affect measurements. The technique appears adequate to measure pHi in the liver and will allow to study pH regulatory mechanisms in the intact organ.

Animals↗
PubMed1991

Role of chloride ions in liver cell volume regulation.

Hypotonic swelling of liver cells is followed by regulatory volume decrease (RVD), which has been shown to involve facilitated release of K+. In this study, the role of C1- in RVD was examined by videoplanimetric analysis of cell volume and measurement of membrane potential (Vm) and resistance (Rm) in single isolated rat hepatocytes, and by measurement of 36Cl efflux in the isolated perfused liver preloaded with the isotope. Liver cells subjected to hypotonic stress by removal of 50 mM external NaCl (70% of control osmolality) swelled from an initial volume of 6.68 +/- 0.77 to 8.27 +/- 0.88 pl (24.3 +/- 3.4% increase) within 1 min and exhibited RVD at an initial rate of 0.26 +/- 0.01 pl/min. A step decrease in external Cl- accelerated the initial rate of RVD to 0.53 +/- 0.08 pl/min. RVD was abolished in cells that had been depleted of Cl-. Vm and Rm displayed biphasic responses to hypotonic stress. An initial (less than 15 s) hyperpolarization of Vm from -35.4 +/- 2.2 to -38.8 +/- 2.6 mV was followed by a gradual depolarization reaching -30.2 +/- 2.0 mV by 1 min. In parallel, Rm initially (less than 15 s) increased from 101 +/- 13 to 121 +/- 17 M omega (19 +/- 3% increase) and then declined to 55 +/- 4 M omega (59 +/- 4% of initial Rm) within 1 min. These changes were reversible upon return to isotonicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Cl(-)-HCO3- exchanger in isolated rat hepatocytes: role in regulation of intracellular pH.

In rat hepatocytes, basolateral Na(+)-H+ exchange and Na(+)-HCO3- cotransport function as acid extruders. To assess mechanisms of acid loading, intracellular pH (pHi) recovery from an alkaline load was analyzed in short-term cultured rat hepatocyte monolayers using the pH-sensitive dye BCECF. Electrophysiological techniques were also used to assess the role of the membrane potential (Vm). Cells were alkaline loaded by suddenly reducing external CO2 and HCO3- (from 10% and 50 mM, respectively, to 5% and 25 mM) at constant pHo. After this maneuver, pHi rapidly rose by 0.13 +/- 0.03 pH units (pHu) and recovered to baseline at an initial rate of 0.026 +/- 0.009 pHu/min. Intracellular buffering power was estimated from the dependence of pHi on [NH4+]o and varied between 70 and 10.5 mM/pHu in a pHi range of 6.5-7.6. Initial pHi recovery corresponded to a rate of OH- efflux (JOH) of 1.76 +/- 0.71 mM/min and was blocked by 0.5 mM DIDS (0.003 +/- 0.002; JOH = 0.18 +/- 0.06) or by 1 mM H2DIDS (0.001 +/- 0.002; JOH = 0.26 +/- 0.08) and by removal of [Cl-]o (0.003 +/- 0.007; JOH = 0.28 +/- 0.07). The dependence of JOH on [Cl-]o exhibited saturation kinetics with an apparent Km for [Cl-]o of 5.1 mM. pHi recovery was Na+ independent and was not inhibited by substitution of Na+ with NMDG (0.045 +/- 0.09; JOH = 2.94 +/- 0.59). During an alkaline load, cell Vm hyperpolarized from -33.4 +/- 1.8 to -43.4 +/- 2.8 mV, mainly due to an increase in K+ conductance by a factor of 2.8 +/- 0.3.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

[Long-term results following subcutaneous Achilles tendon rupture].

From 1972 to 1982, 132 ruptures of the achilles tendon were treated at the Orthopedics Division, University of Heidelberg. Surgical treatment was carried out in 125 cases, and seven patients were treated conservatively. The average age of the patients was 42 years. 84% of the achilles tendon ruptures occurred during sport. After an average investigation period of 6.5 years, 33 patients could be followed up. The rate of complications and the final functional results are communicated. The blood supply to the achilles tendon is described separately. Twelve cadaver achilles tendons were investigated by means of the plastination method. It could be demonstrated that a reduced blood supply to the Achilles tendon is present about 3-5 cm above the calcaneal tuber. This finding corresponds to the most frequent site of rupture. It is unclear to what extent there is a connection between the blood supply and the rupture site of typical locations.

Achilles Tendon↗
PubMed1990

[Microcirculation of the Achilles tendon and significance of the paratenon. A study with the plastination method].

Rupture of a healthy Achilles tendon is disputed. A previous degenerative process with ischemia after recurrent microtraumas is usually held to be responsible. The vascular anatomy of eight human specimens was defined with a new method after perfusion through the femoral artery. This method allows exact analysis of the vessels even at a microscopic level. In contrast with the literature, the authors found a large number of anastomoses between the extra- and the intratendinous vessel system. The well-vascularized paratenon is therefore very important for the nutrition of the Achilles tendon. This fact must be taken into account during the surgical treatment of a rupture. The authors agree with the studies of the anatomist Lang who found a decrease of the intratendinous vascularization in an area 3 to 5 cm above the insertion in the os calcis. However a relationship between the frequency of rupture in this area and the vascular anatomy has not yet been shown.

Achilles Tendon↗
PubMed1990

[Joint chondromatosis. Results in 40 surgically and conservatively treated patients].

The clinical findings seen in chondromatosis (Henderson-Jones syndrome) and the treatment of this rare disease are presented. The etiology is also discussed. The authors suggest a therapy, drawing on their own experience in 40 patients with an average follow-up of 12.6 years and on numerous articles from the literature. They recommend total synovectomy with removal of loose bodies at an early stage to prevent mechanical destruction of articular cartilage.

Adult↗
PubMed1989

Hepatobiliary transport of the anionic organomercury compound (mersalyl) is carrier mediated.

The hepatobiliary excretion of the anionic organic mercury compound (mersalyl) was studied in the isolated perfused rat liver and in isolated rat liver plasma membrane vesicles. In the isolated perfused liver, mersalyl is immediately taken up from the perfusion medium and concentratively excreted into bile. Uptake is characterized by saturation kinetics (S)0.5 = 20 microM, Vmax = 117 nmoles/min/g liver, cooperatively of mersalyl binding sites, stimulation by extracellular sodium and temperature dependence. Uptake of mersalyl into basolateral membrane vesicles also exhibits characteristics of a carrier mediated transport: saturation kinetics (S)0.5 = 28 microM, Vmax = 1.6 nmoles/min/mg protein, dependence on extravesicular sodium, cooperativity of mersalyl binding sites, temperature dependence and transstimulation by intravesicular non-radioactive mersalyl. Uptake was inhibited by alpha-naphthylacetic acid and mercapto group reagents, indicating involvement of mercapto groups on the carrier and a binding site for carboxylic anions. Data from the isolated perfused liver and from isolated basolateral vesicles indicate that mersalyl uptake into the liver is carrier mediated. Uptake mechanism and driving forces appear analogous to those for the uptake of chemically related compounds such as taurocholic acid. Therefore it is speculated that mersalyl may be transported by carrier molecules which apparently accept numerous chemically unrelated compounds.

Animals↗