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R M Henderson

Publications and source records attributed to R M Henderson.

At least 55 records · Page 3Linked to original sources
PubMed1987

Na-H exchange regulates intracellular pH in isolated rat hepatocyte couplets.

Intracellular pH (pHi) was measured directly in isolated rat hepatocyte couplets using pH sensitive microelectrodes. The hepatocytes were maintained in a minimal salt buffer without added hormones or serum. Values of pHi (6.99 +/- 0.12, mean +/- SE) were close to their Nernst equilibria. After intracellular acidification with ammonium chloride, pH regulation was inhibited with 1 mM amiloride or by omission of external sodium, consistent with a Na-H exchange mechanism. Mean intracellular buffering power, in the nominal absence of carbon dioxide, was 34.1 +/- 11.4 mM. In the presence of external bicarbonate, amiloride or omission of sodium slowed, but did not completely inhibit recovery from acidification, indicating that additional pHi regulation mechanisms may operate in this preparation. These studies provide a direct measurement of pHi in hepatocyte couplets and indicate that Na-H exchange, together with a bicarbonate dependent system are important mechanisms for pHi regulation in this preparation.

Amiloride↗
PubMed1986

Measurement of intracellular pH with microelectrodes in rat kidney in vivo.

The construction of two types of double-barreled microelectrodes of sufficiently small tip size to record cytosolic pH (pHc) in renal tubular epithelial cells is described. Mean pHc in control anesthetized rats was 7.10 and mean basolateral membrane potential (Em) was -51.8 mV. These results suggest that hydrogen ions are actively extruded from either or both poles of the proximal tubular cell but that bicarbonate exit across the basolateral membrane is passive. In animals treated with acetazolamide, pHc was significantly elevated (mean 7.35) but Em was unchanged, suggesting that proton extrusion continues but that the rate of reaction of OH- with CO2 is diminished due to carbonic anhydrase inhibition. A pH higher than that of arterial blood was obtained from sites presumed to be in the interstitium. The evidence for the various assignments of microelectrode tip position is discussed.

Acetazolamide↗
PubMed1984

L(+)-Lactate binding to preparations of rat hepatocyte plasma membranes.

Incubation of rat hepatocyte plasma membranes with L-[14C]lactate resulted in the labeling of protein(s) of apparent molecular weight 40,000 when examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The binding was saturable, irreversible, and inhibited by pyruvate, 2-oxoglutarate, and alpha-cyano-3-hydroxycinnamate, but not by D-lactate. It was markedly enhanced by L-alanine, but not D-alanine or beta-alanine. The binding protein(s) could be solubilized in cholic acid giving a single peak on gel filtration corresponding to a molecular weight of 26,000 and an isoelectric point of 5.1. This peak, when subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, ran in a position corresponding to an apparent molecular weight of 40,000. When membranes were treated with Triton X-100, lactate binding was retained by the Triton-insoluble fraction. The binding of L-[14C]lactate increased with incubation time, due apparently to the appearance of new binding sites and not to sequestration into vesicles. As many of the characteristics of lactate binding to rat hepatocyte plasma membranes were found to be similar to those of lactate entry into isolated hepatocytes, we speculate that the lactate-binding protein could represent part or whole of a plasma-membrane lactate transporter. Lactate-binding proteins of the same molecular weight were identified in the plasma membranes from rat erythrocytes, cardiac muscle, skeletal muscle, lung, and brain.

Animals↗
PubMed1984

The mechanism of inhibition of ureogenesis by acidosis.

In perfused rat liver a decrease of cytosol pH, determined with pH-sensitive microelectrodes, from 7.2 to 6.85 is associated with a 50% fall in ureogenesis from ammonium chloride. In isolated rat hepatocytes the fall in ureogenesis due to acidosis is associated with decrease in the mitochondrial and cytosolic concentration of citrulline. Limitation of carbamoyl phosphate synthesis and thus citrulline supply could be responsible for the inhibition of ureogenesis observed.

Acidosis↗
PubMed1982

The techniques and uses of intracellular pH measurements.

Weak-acid, 31P-nuclear magnetic resonance (NMR) and microelectrode techniques for measuring intracellular pH (pHi) are compared by demonstration of their use in rat liver. The ultimate test of suitability of these methods is the confidence with which they can be used to clarify aspects of metabolic regulation, translocation of substances across biological membranes, and the control of cell pH itself. Though resting pHi in perfused liver is fairly similar with all three techniques, substantial quantitative differences between values obtained with 31P NMR and microelectrodes are revealed after addition of fructose to the perfused liver preparation. The use and limitations of weak-acid methods in determining the mechanism of inhibition of gluconeogenesis from lactate by acidosis and in determining the pH responsiveness of the lactate transporter in the hepatocyte plasma membrane are demonstrated. Microelectrode-derived values of pHi are probably referable to the bulk phase of the cytosol, whereas values from the other two methods are more complex in their interpretation. Microelectrode and NMR methods have the great advantage of being non-destructive, and continuous records may be obtained.

Animals↗
PubMed1982

Coalignment of the muscle cell and nucleus, cell geometry and Vv in the tunica media of monkey cerebral arteries, by electron microscopy.

We undertook to ascertain how well aligned is the rod-shaped nucleus within the spindle-shaped cell of vascular muscle in order that we might use the darkly staining nucleus in histological sections to indicate precisely the directional alignment of the cell. We fixed cerebral arteries from five monkeys under physiological pressure and embedded portions of the tissue so that mid-plane longitudinal sections of the arteries were obtained; the circumferentially arranged muscle cells were cut in cross-section. From the electron micrographs we obtained the cross-sectional profile of the cell and its nucleus, determining that the centre of the nucleus was on average 9.5 +/- 5.8% (SD) away from the centre of the cell (expressed as a ratio of the cellular diameter). We calculated the alignment between the cell and nucleus to be from 0 to 3 degrees, and obtained a volume fraction of 59% for muscle tissue in the tunica media of these arteries.

Animals↗
PubMed1982

Metabolic inter-relationships of intracellular pH measured by double-barrelled micro-electrodes in perfused rat liver.

1. Intracellular pH (pHi) was measured under differing conditions in the functionally isolated, perfused rat liver using double-barrelled recessed-tip micro-electrodes. 2. Under normal acid-base conditions mean hepatic pHi was 7.18. 3. Over the range studied, hepatic pHi was negatively and linearly related to the logarithm of perfusate PCO2. 4. Measurement of pHi together with measurement of pHe and intracellular and extracellular lactate concentrations suggested a non-equilibrium distribution of lactate and lactic acid across the hepatic cell membrane requiring an active transport process for entry of lactate to the cell. 5. Upon addition of D-fructose (10 mM) to the perfusate there was a rapid fall in pHi of between 0.2 and 0.54 units, which was substantially greater than observed in earlier similar experiments in which 31P-nuclear magnetic resonance was used to measure pHi. Reasons for this discrepancy are considered.

Animals↗
PubMed1981

The effect of adrenaline on hepatic lactate uptake in the acidotic partially ischaemic rat liver.

1. The effect of adrenaline (7 X 10(-8) and 7 X 10(-7) mol/l) on lactate uptake and glucose output was studied in the perfused liver of starved rats under conditions of reduced flow and acid perfusate. 2. Adrenaline largely prevented the decrease in hepatic lactate uptake which would otherwise occur owing to reduced blood flow and acidosis and may, therefore, have a protective effect in strenuous exercise and shock.

Acidosis↗
PubMed1976

Cell contacts and distribution of nerves in the smooth muscle of estrogen-dominated rabbit oviduct.

The types of cell-to-cell contacts and the relationship between the nerve endings and the smooth muscle of the estrogen-treated rabbit oviduct have been investigated. The cell contacts most consistently found in the oviduct were simple appositions, with a 20-nm cell separation, which occasionally included a more dense region, and interdigitations of muscle cell processes with the same separation distances. Very rarely, wider intermediate contacts were present. Gap junctions (nexuses) were absent. It seems likely that simple appositions and interdigitations form the low resistance pathway for conduction of electrical activity. Nerves containing small dense-cored vesicles were present both within and near muscle bundles; they were rarely found close to smooth muscle cells.

Animals↗
PubMed1975

D2 18O (deuterium oxide) method for CO2 output in small mammals and economic feasibility in man.

A test of the validity of the isotopic steady state relationships of the doubly labeled water (H2O) method has been carried out with D2 18O in small mammals (three chipmunks and one mouse). CO2 outputs calculated just from 1) the rate of water intake and 2) the ratios of the isotopic concentrations in the body water to the intake water agreed satisfactorily with observed values. Moreover, reconstructed energy and material balances agreed reasonably with similar balances reconstructed for an immediately succeeding period on the same animals studied by the previously validated decay procedure. We conclude from an error analysis that by expressing the isotopic specific activities as abundances in excess of the body water of a subject on a given regimen, the decay procedure is economically feasible in the human with available accuracy of isotopic analyses and the present cost of H2 18O. The method therefore appears to be a useful tool ready for application to the field of human energy metabolism.

Animals↗