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Biomedical subjects

W S Rehm

Publications and source records attributed to W S Rehm.

At least 37 records · Page 2Linked to original sources
PubMed1987

Inhibition of acid secretion of fundus of Rana pipiens with a high concentration of potassium on the secretory side.

Inhibition of acid secretion of the frog fundus is generally accompanied by an increase in transmucosal resistance, Rt, and in potential difference, PD (nutrient normally positive). These results are predicted for the intact tissue by an electrogenic proton pump. It has been suggested that the increase in PD with inhibition can also be explained by a neutral proton pump. The latter model postulates a K+ diffusion potential across the secretory (lumen-facing) membrane tending to make the secretory side positive. Upon inhibition, the [K+] in the lumen is assumed to increase, which decreases the diffusion potential, resulting in an increase in the positivity of the nutrient side. To test this theory, we determined the effects of inhibition with a high [K+] on the secretory side. With a high [K+] in the lumina, inhibition would result in only a small change in the ratio of K+ in the cell to that in the lumina, and hence a small change in the diffusion potential. We found, however, that inhibition increased the PD essentially the same as in the controls. With inhibition the resistance also increased with high secretory K+. Elevating the secretory K+ during secretion produced a 44% decrease in Rt indicating a large increase in luminal K+. We conclude that the results are not compatible with the K+ diffusion potential model but are those predicted by the electrogenic concept.

Animals↗
PubMed1987

Potential difference responses to secretory K+, Na+ and HCO3- changes in secreting and resting states of frog stomach in Cl(-)-free media.

The effects of changes in secretory concentrations of K+, Na+ and HCO3- on transmucosal potential difference (PD) and resistance in Cl(-)-free (SO4(2-)) solutions were compared for secreting fundus and resting fundus of Rana pipiens. In the resting fundus experiments, histamine was not present in the nutrient solution and cimetidine was primarily used to obtain acid inhibition. Increase of K+ from 4 to 80 mM, decrease of Na+ from 156 to 15.6 mM and decrease of HCO3- from 25 to 5 mM gave, 10 min after the change, in the secreting fundus delta PD values of 39.7, -11.9 and 3.2 mV, respectively. In the resting fundus, 1.5 to 2 h after the addition of cimetidine, the same changes in secretory ion concentration gave delta PD values of 12.2, -5.6 and 1.5 mV, respectively. Replacement of cimetidine with SCN and without histamine yielded a delta PD somewhat lower than that in cimetidine, namely 9 mV for a K+ change from 4 to 80 mM. Subsequent addition of histamine with SCN present gave a delta PD of about 21 mV. The change in PD was attributed to histamine increasing the secretory membrane area, leading to an increase in K+ conductance. Another possibility is that histamine increases the K+ conductance per se.

Animals↗
PubMed1986

Amphotericin B enhanced anomalous potential difference response to changes in aqueous K+ in frog cornea.

An increase in aqueous K+ from 0 to 4 mM increased the potential difference (anomalous response of electrogenic (Na+ + K+)-ATPase antiport) by 1.1 mV in Cl(-)-free solutions compared to 6.8 mV in Cl- solutions. With amphotericin B added to the tear solution in Cl(-)-free solutions, the anomalous PD response for the addition of 4 mM K+ to the aqueous solution was about 20 mV, significantly greater than in Cl- solutions. This anomalous response was inhibited by ouabain. These data support the electrogenicity of the (Na+ + K+)-ATPase pump. It is also evident that, for the pump to respond, Na+ should readily enter the cell. This may be accomplished experimentally, either across the basolateral membrane in Cl- solutions or across the apical membrane in Cl(-)-free solutions with amphotericin B present in the tear solution.

Amphotericin B↗
PubMed1986

Effects of NaSCN and omeprazole on resistance and potential of fundus of Rana pipiens.

Thiocyanate (SCN) produced a rapid inhibition of acid secretion and a concurrent rapid increase in the transmucosal potential difference (PD) and resistance. After inhibition, resistance rapidly peaked and then decreased. In contrast, omeprazole produced a slow inhibition of secretion and a slow increase in PD and resistance. The peak increase in resistance with SCN was significantly greater than the steady-state increases for both SCN and omeprazole. All increases were significant. The increases in PD and resistance are greater at high H+ rates than at low H+ rates. We postulate that the peak SCN increase in resistance is due to the increase in resistance of the secretory membrane, which is followed by a decrease in resistance of the nutrient membrane. On this basis the omeprazole increase in resistance that occurs concurrently with the slow decrease in the H+ rate is a result of a concurrent change of the resistances of the two opposing membranes.

Animals↗
PubMed1986

Sites of resistance changes with inhibition of acid secretion in frog stomach.

The primary purpose of this study was to determine the sites of resistance changes from thiocyanate inhibition of secretion to better evaluate models of the gastric proton pump. The potential difference, resistance, and H+ secretory rate were measured with various tonicities of the secretory fluid. Thiocyanate (SCN) inhibition generally produces a resistance increase, but with nutrient Ba, the resistance is high and SCN decreases it. The latter effect is also seen with cimetidine. In the secreting fundus a hypotonic secretory solution has a small effect on resistance, but in the inhibited fundus the effect is huge, due to increase of resistance of the lumen-tubular cell pathway. With a hypotonic secretory solution, for inhibited fundus (cimetidine or omeprazole) and antrum, SCN does not decrease the resistance of the surface cells and/or the transintercellular pathways with or without Ba. The SCN resistance decrease with Ba is via the tubular cell pathway. With Ba the resistance of the nutrient membrane of the tubular cells decreases after SCN or cimetidine inhibition. The findings further support the concept that under standard conditions the resistance via the lumina and tubular cells is low and that via the surface cells and transintercellular pathways is high.

Animals↗
PubMed1985

Effect of Ba2+ on the K+ conductance pathways in the frog cornea.

Two types of transepithelial potential difference (PD) responses have been observed in the bullfrog, Rana catesbeiana, when the K+ concentration is changed in the aqueous solution. (1) A normal response, that is, a decrease in the positivity of the aqueous solution when the K+ is increased in this solution. (2) An anomalous response, that is, an increase in PD when K+ is increased from 0 to 4 mM in the aqueous solution. In present experiments 2 mM Ba2+ results in a significant decrease in transepithelial PD and an increase in resistance (R), consistent with the well-known effect of Ba2+ on the K+ conductance in other biological membranes. In the presence of Ba2+ compared to its absence the normal PD responses were decreased when K+ was increased from 4 to 20 or to 79 mM in the aqueous solution. Barium enhanced, but not significantly, the anomalous PD response (PD increase) when K+ was increased from 0 to 4 mM. An anomalous PD response (PD decrease) was obtained with Ba2+ when K+ was changed from 4 to 0 mM while in its absence the response was normal (PD increase) or did not change. These findings support the concept that anomalous PD responses as a result of the electrogenic (Na+ + K+)-ATPase may be obtained when the resistance of the simple K+ pathway is increased.

Animals↗
PubMed1985

Evidence for HCO3- conductance pathways in nutrient membrane of bullfrog antrum.

The effect of changing the nutrient HCO3- concentration on potential difference (PD) and resistance in bullfrog antrum bathing in CI- media was determined. Changes in HCO3- concentration were from 25 mM to several lower concentrations and back to 25 mM. A plot of /delta PD/ versus log [HCO3-] gave a linear relation for changes of HCO3- concentration from 25 down to 3.1 mM and back to 25 mM but deviated to some extent for changes to 1.6 mM. In these experiments, changes from higher to lower HCO3- concentrations gave a less rapid initial PD response than those in the reverse direction. This result eliminated H+ conductance pathways as being predominant. Experiments were done in which in the first part changes were made in nutrient solution from 5 percent CO2 and 25 mM HCO3- to 0.6 percent CO2 and 3 mM HCO3- and in the second part the same changes with a simultaneous changes of secretory solution from 5 percent to 10 percent CO2. The magnitude of PD decrease was greater by 4.5 mV in the second part. This result indicated that HCO3- conductance pathways rather than OH- conductance pathways are predominated . There was no evidence of HCO3-, OH-, and H+ conductance pathways in secretory membranes.

Animals↗
PubMed1985

Electrogenicity of the Na-K-ATPase pump in bullfrog cornea epithelium.

The effect of changing the K concentration in the aqueous solution was studied in the frog cornea. In general, when the K concentration was increased from 4 to 20 or 79 mM, the transepithelial PD and resistance decreased. If K was decreased from 79 to 4, 20 to 4, or 4 to 0 mM, or any other combination, the PD and resistance increased. These are normal PD responses. If after a K-free period of more than 5-10 min the K was increased to 4 mM, the PD increased, an anomalous PD response. If K was increased from 0 to 20 mM, there was an initial PD increase (anomalous response) followed by a PD decrease (normal response). If K was increased from 0 to 79 mM the PD decreased, normal response only. The resistance decreased with every increase in K concentration. Anomalous responses were abolished in Na-free solutions and in the presence of both 10(-3) M ouabain and 10(-4) M vanadate in the aqueous solution. We interpret the results on the basis of two pathways, a simple K-conductive pathway and an electrogenic Na-K-ATPase pump pathway with more Na's than K's per cycle. The normal or anomalous PD responses to changes in aqueous K concentration depend on the relative resistance of the two pathways.

Animals↗
PubMed1984

Effect of reduced pH in absence of HCO3(-) on anomalous and normal potential responses in bullfrog antrum.

Effect of changing [K+], [Na+] and [Cl-] in nutrient solution on potential difference (PD) and resistance was studied in bullfrog antrum with and without nutrient HCO3(-) but with 95% O2/5% CO2 in both cases. In both cases, changing from 4 to 40 mM K+ gave about the same initial PD maximum (anomalous response) which was followed by a decrease below control level. Latter effect was much less with zero than with 25 mM HCO3(-). Changing from 102 to 8 mM Na+ gave initial normal PD response about the same in both cases. However, 10 min later the change in PD with zero HCO3(-) was insignificant but with 25 mM HCO3(-) the PD decreased (anomalous response of electrogenic NaCl symport). PD maxima due to K+ and Na+ were largely related to (Na+ + K+)-ATPase pump. Changes in nutrient Cl- from 81 to 8.1 mM gave only a decrease in PD (normal response). Initial PD increases are explained by relative increases in resistance of simple conductance pathways and of parallel pathways of (Na+ + K+)-ATPase pump and Na+/Cl- symport. Removal of HCO3(-) and concurrent reduction of pH modify resistance of these pathways.

Animals↗
PubMed1984

Potential difference responses due to K+, Na+ and Cl- changes in bullfrog antrum with and without HCO3-.

The effect of changing [K+], [Na+] and [Cl-] in nutrient solution was studied in bullfrog antrum with and without HCO3- in nutrient. In 25 mM HCO3- (95% O2/5% CO2) and in zero HCO3- (100% O2), nutrient pH was maintained at 7.3. Changing from 4 to 40 mM K+ or from 81 to 8.1 mM Cl- gave a decrease 10 min later in transmucosal PD (nutrient became more negative)--a normal response. These responses were less in zero than in 25 mM HCO3-. A decrease from 102 to 8 mM Na+ decreased PD (anomalous response of electrogenic NaCl symport). This effect was attenuated or eliminated in zero HCO3-. In contrast, change from 4 to 40 mM K+ gave initial anomalous PD response and change from 102 to 8 mM Na+, initial normal PD response with either zero or 25 mM HCO3-. Both responses were associated with (Na+ + K+)-ATPase pump and were greater in zero than in 25 mM HCO3-. Initial PD increases in zero HCO3- are explained as due to increase in the resistance of passive conductance and/or NaCl symport pathways. Thus, removal of HCO3- modifies conductance pathways of nutrient membrane.

Animals↗
PubMed1983

Normal and anomalous potential responses due to K+ changes in bullfrog antrum.

The effect of changing the K+ concentration in the bathing media was studied in the bullfrog antrum. Usually increasing K+ on the nutrient side in standard Cl- -containing and Cl- -free solutions decreased the transmucosal potential difference (nutrient became more negative) - a normal effect. Similar results were obtained on the secretory side. Moreover, for K+ changes on the nutrient side in Cl- media, a plot of magnitude of delta V vs. log [K+] was linear for [K+] greater than 20 mM with slope of 27 mV per 10-fold change in [K+]. However, after bathing the mucosa in Cl- media with zero K+ for about 20 min, elevating the nutrient [K+] to 4 mM increased the potential difference (V) by 4.8 mV in 5 min and repeating the same sequence increased V by 6.9 mV in 5 min - both anomalous effects. Beyond 20 mM K+ the response was normal. In SO2-4 media, an anomalous potential difference of about 1 mV was obtained for changes from 0 to 3 or 6 mM nutrient K+. Ouabain (1 X 10(-3) M) in the nutrient solution abolished the anomalous response in Cl- and SO2-4 media. The normal response is attributed to passive, conductance pathways and the anomalous response because of the effect of ouabain, to a (Na+ + K+)-ATPase pump on the nutrient-facing membrane in which more Na+ than K+ ions are transported per cycle.

Animals↗
PubMed1983

Mechanisms responsible for SCN increase in resistance of in vitro frog gastric mucosa.

Thiocyanate (SCN) inhibits H+ secretion and increases the resistance and potential difference (PD) of the gastric mucosa. These results support our separate-site electrogenic theory of HCl secretion. Recent work shows that an ATP-driven mechanism in the gastric mucosa can produce H+ by a neutral exchange of K+ for H+. The SCN increase in resistance and PD, if due to an inhibition of a high-conductance mechanism(s) in the secretory plasma membrane, is not easily compatible with the neutral mechanism. Therefore, the possibility was examined that SCN induces the increase in resistance by other mechanisms. The HCl and NaCl concentration profiles in the pit and tubular lumina were calculated. The effects of SCN were determined with isotonic, hypotonic, hypertonic, buffered, and high [H+] secretory solutions. The results indicate that SCN produces an increase in resistance of about 130 omega. cm2 of the plasma membranes of the tubular cells. A scheme is proposed that incorporates the neutral K+-H+ mechanism into an electrogenic system.

Animals↗
PubMed1983

Anomalous potential difference responses to changes in sodium concentration in the antrum of frog stomach.

Previously, an electrogenic Na-Cl symport was found in the fundus, and the question arises of whether there is one in the antrum, a tissue that does not secrete acid. In an in vitro preparation of the antrum of Rana catesbeiana, we found that when the [Na+] in nutrient solution was decreased (choline for Na+) the transmucosal potential difference (PD) decreased (the positivity of nutrient side decreased), and when the [Na+] was increased the PD increased. These PD changes were anomalous for Na+ but not for choline. A linear relationship for PD versus log [Na+] and not versus log [choline] excluded a choline conductive pathway. The anomalous PD response was decreased but not abolished by 10(-3) M ouabain. Normal PD responses resulted from [Na+] changes in Cl--free (SO2-4) solutions. PD responses to changes in nutrient [Cl-] were normal but decreased in the absence of Na+. Data are compatible with a passive electrogenic Na-Cl symport with more chloride than sodium ions transported per cycle, as in the fundus. Symport conductance-to-total Cl- conductance ratio is higher in antrum than in the fundus. Data from the luminal side were compatible with apical membrane conductances for Na+ and Cl-.

Animals↗
PubMed1982

Evidence for electrogenic Na-Cl symport in the in vitro frog stomach.

The transmucosal potential difference (PD) response to step changes in Na+ (choline or Mg2+ for Na+) in the nutrient fluid was studied. Decreasing the Na+ concentration in the nutrient fluid decreased the positivity of the nutrient side, and increasing the Na+ concentration increased the positivity. This effect is anomalous because it is opposite to that of a simple Na+ conductive pathway but right for a choline or Mg2+ conductive pathway. The lack of linearity of delta PD versus the log of the choline concentration ruled out a choline conductive pathway. An approximate linear relation was obtained for Na+. The anomalous PD response for Na+ was reduced but not abolished in 1) K+-free bathing fluids and 2) 10(-3) M ouabain in nutrient fluid. Changing the Cl- concentration in nutrient fluid gave normal PD responses, which were reduced in the absence of Na+. These results are attributed to a passive electrogenic Na-Cl symport. Theoretical considerations, for p Na+ and q Cl- transported per cycle (with q greater than p), predict an anomalous delta PD for Na+ concentration changes and a normal delta PD for Cl- concentration changes.

Animals↗
PubMed1981

Anomalous potential response and (Na+ + K+)-ATPase in in vitro frog gastric mucosa.

In general, increasing K+ on the nutrient side decreases the transmucosal PD (nutrient becomes more negative) but after bathing the mucosa in zero K+ media for about 30 min, or longer, elevation of K+ on the nutrient side increases the PD, an anomalous effect. In Cl- media, increasing nutrient K+ from zero to 4 mM produces an increase in PD (an anomalous response) of 3.1 and 5.3 mV in 2 and 5 min, respectively. Ouabain (10(-3) M) to the nutrient side abolished the anomalous response as did removal of Na+ (choline for Na+) from bathing media. In SO4(2-) media (SO4(2-) for Cl-), a significant anomalous PD response was observed when K+ on the nutrient side was increased from zero to 1, 2 or 3 mM but not to higher K+ concentrations. In this case, ouabain also abolished the anomalous response. It is postulated, on the basis of the effects of ouabain and the use of choline media, that an electrogenic (Na+ + K+)-ATPase pump is present on the nutrient-facing membrane in which more Na+ than K+ are transported per cycle.

Animals↗
PubMed1981

Effects of ouabain on frog gastric mucosa in vitro.

The effect of the addition of ouabain to the nutrient solution was determined on resistance, potential difference (p.d.) and H+ secretion rate. In NaCl media, 10(-3) M ouabain decreased significantly the p.d. from 25.6 mV to 16.1 mV in 30 min and to 11.0 mV in 60 min. No significant changes occurred in resistance and H+ secretion rate. In Na2SO4 (Cl(-)-free) media, ouabain produced a biphasic effect on p.d. The p.d. changed from -28.0 mV (nutrient-negative) to a nadir of -37.4 mV in 7 min and then increased to -16.4 mV in 60 min. At the nadir there was no significant change in resistance or H+ secretion rate but at 60 min, unlike Cl- media, resistance increased by 36% and H+ secretion rate decreased by 43%. To decide whether the ouabain-caused decrease in H+ rate in Na2SO4 media was due to an effect on the H+ pump or on resistance of the return pathways, the voltage was clamped at 0 and 40 mV. Clamping the voltage showed that in the case of a marked decrease in the H+ secretion rate, the H+ transport mechanism itself was inhibited (and not the parallel pathway). The decrease in p.d. due to ouabain in Cl- and SO42- media indicates that the (Na+ + K+)-ATPase mechanism may be electrogenic.

Animals↗