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R Beauwens

Publications and source records attributed to R Beauwens.

43 records · Page 3Linked to original sources
PubMed1981

Effects of vanadate on the functional properties of the isolated toad bladder.

1. Vanadate, considered by some as a candidate for physiological modulation of Na pumping activity, was studied in the isolated toad urinary bladder. It produced a decrease in Na transport activity that was reversible and could be partially antagonized by pretreatment with a disulphonic distilbene derivative, SITS. This suggests an intracytoplasmic site of action for vanadate. Other transition metal salts, prepared from Ta and Nb, produced instead a transient rise in Na transport and this was unaffected by SITS. 2. Comparison between ouabain and vanadate showed clear-cut differences: inhibition of Na transport by the former, not the latter, was partially overcome by increasing of Na transport by the former, not the latter, was partially overcome by increasing cell Na or serosal K. Unexpectedly intracellular K did not decrease appreciably following vanadate treatment, in contrast to what occurs when ouabain was used instead. 3. Vasopressin-induced hydro-osmotic flow was irreversibly inhibited by vanadate but not by ouabain; pretreatment with SITS attenuated this effect. Moreover, vanadate blocked urinary acidification in this epithelium, thus supporting the hypothesis that proton flow occurs through an enzyme distinct from the mitochondrial ATPase, insensitive to vanadate.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1978

Evidence for a transcellular component to the transepithelial sodium efflux in toad skin.

The transepithelial efflux of sodium, from the inner to the outer surface was measured across the isolated toad skin, mostly after abolition of the electrochemical gradient. The effects on this efflux of several agents and manipulations were studied in order to make a distinction between the paracellular component and a hypothetical transcellular one. Amiloride decreased the transepithelial efflux, while ouabain and cyanide increased it. From the known mode of action of those agents, it was inferred that part of the efflux occurred across the cell. Removal of sodium from the external solution interfered apparently with both components of the transepithelial efflux, while the action of external hypertonicity seemed to be restricted to the paracellular shunt pathway. Access of sodium from the internal solution to the active transport pool is thus suggested, with consequent increase in metabolic cost of transport. Yet, compared with the net influx, the amounts involved are very small; consequently, they escape detection by oxygen consumption measurements.

Amiloride↗
PubMed1976

Active H+ transport in the turtle urinary bladder. Coupling of transport to glucose oxidation.

The turtle urinary bladder acidifies the contents of its lumen by actively transporting protons. H+ secretion by the isolated bladder was measured simultaneously with the rate of 14CO2 evolution from [14C]glucose. The application of an adverse pH gradient resulted in a decline in the rate of H+ secretion (JH) and in the rate of glucose oxidation (JCO2). The changes in JH and JCO2 were linear functions of the pH difference across the membrane. Hence, JH and JCO2 were linearly related to each other. The slope, deltaJH/deltaJCO2 was found to be similar in half-bladders from the same animal but was seen to vary widely in a population of turtles. To investigate the effect of pH gradients on deltaJH/deltaJCO2, two experiments were performed in each of 14 hemibladders. In one, JH and JCO2 were altered by changing the luminal pH. In the other, they were altered by changing the ambient pCO2 while the luminal pH was kept constant. The average slope, deltaJH/deltaJCO2, in the presence of pH gradients was 14.45 eq-mol-1. In the absence of gradients in the same hemibladders it was 14.72, delta = 0.27 +/- 1.46. The results show that H+ transport is organized in such a way that leaks to protons in parallel to the pump are negligible. Analysis of the transport system by use of the Essig-Caplan linear irreversible thermodynamic formalism shows that the system is tightly coupled. The degree of coupling, q, given by that analysis was measured and found to be at or very near the maximum theoretical value.

Acetazolamide↗
PubMed1976

Further studies on coupling between sodium transport and respiration in toad urinary bladder.

When sodium transport (JNa) and CO2 production (JCO2) were measured simultaneously in the toad urinary bladder in the absence of electrochemical gradients under conditions of spontaneous variation of JNa, the curve of JNa on JCO2, phiJNa/phiJCO2, was found to be highly linear in an individual epithelium. However, no unique value appeared to characterize a population of bladders. In an effort to investigate the nature of this variation, phiJNa/phiJCO2 was examined under a variety of conditions. It was found that agents that affect sodium entry into the active transport pool, e.g. vasopressin and amiloride, or those that influence the energy-linked exit step, e.g. ouabain and insulin, have no effect on the phiJNa/phiJCO2. To investigate the possibility of the presence of a significant backleak from the serosal side into the cell, the sodium concentration was changed to 75 and 160 mM. Neither of these maneuvers influenced phiJNa/phiJCO2 or (JCO2)JNa=O. Furthermore, in the absence of mucosal sodium, ouabain had no effect on JCO2, suggesting that no significant recirculation is occurring. It is concluded that for each individual epithelium JNa is coupled to JCO2, and their ratios appear, within experimental error, to be invariant. It is suggested that sodium traverses the active transport pathway largely or entirely in one direction.

Animals↗
PubMed1975

Coupling of sodium transport to respiration in the toad bladder.

Energy expenditure and transepithelial sodium transport were measured continuously and simultaneously from isolated urinary bladders of the Dominican toad, Bufo marinus. Sodium transport was measured as the short-circuit current and CO2 produced by the bladder was measured conductometrically by the method of Maffly. The rates of sodium transport and CO2 productions were linearly related. The slope of the regression of sodium transport on CO2 production, dJNa/dJCO2, was found to be quite similar in paired half bladders but to differ significantly between bladders from different toads. Thus, in this preparation there appears to be no unique stoichiometric ratio characterizing sodium transport and metabolism and past efforts to arrive at such a value by averaging results obtained from different animals do not seem warranted. The CO2 production by the isolated bladder which is unrelated to sodium transport was determined by two means: 1) extrapolating the regression of JNa on JCO2 to JNa equals O, and 2) measuring CO2 production with sodium transport suppressed by removal of all sodium from the mucosal bathing medium. The two methods gave values which were in close agreement in each preparationmthis suggests that metabolism which supports nontransport activities in this tissue cannot be recruited to support the energy requirement of sodium transport and vice versa.

Animals↗