Net Potassium Flux Research Articles

Action of histamine on the permeability of the frog gastric mucosa to potassium and water

The permeability to potassium and water of the isolated gastric mucosa of the frog, Rana pipiens, has been studied. Measurements were realized in spontaneously secreting and histamine (2·10 −5 M) stimulated mucosae in vitro. Electrical potential differences and net potassium fluxes were measured in solutions containing known potassium concentrations. Permeability coefficients for potassium of 11.8·10 −6 and 22.6·10 −6 cm/sec were calculated for the spontaneously secreting and histamine-stimulated mucosae, respectively. A diffusion permeability coefficient for water of 0.42·10 −4 ml/cm 2·sec, was obtained for the spontaneously secreting mucosa using 3H-labelled water; addition of histamine did not change the water diffusion rate. Values of 2.2·10 −2 and 3.7·10 −2 cm 4/sec per mole of glucose were obtained for the permeability coefficient for water filtration in the spontaneously secreting and histamine-stimulated mucosae, respectively. From these findings, it may be concluded (a) that stimulation with histamine increases the permeability of the mucosa to potassium and to water filtration, and (b) that the main barrier for the diffusion of water and that for filtration of water are different, the one for diffusion being insensitive to histamine at the concentration used.

Transport of potassium by the gastric mucosa of the frog.

The transport of potassium across the isolated frog gastric mucosa was studied by the chamber method. The net flux of potassium from the nutrient to the secretory phase ( JnsK) did not follow the predictions of simple passive diffusion when the mucosa was incubated with equivalent concentrations of K+ in the secretory and nutrient phases. Furthermore, a net gain in secretory potassium occurs against the electrochemical potential gradient if the mucosa is first incubated with nutrient solutions containing 4 mEq/1. of K+. Neither the loss of K+ from mucosal cells nor solvent drag appears to account for the positive values of JnsK under these circumstances. These data indicate, therefore, that there is a small but significant component of active potassium transport in this preparation.

Relationship between potassium, acid secretion and bioelectric potentials of frog gastric mucosa in the presence of histamine and thiocyanate.

The transmucosal potential difference (PD), the rate of H+ secretion and the net flux of potassium from nutrient to secretory phases (JnsK) of the frog gastric mucosa were studied in vitro by the chamber method. Histamine produced a fall in PD, a sustained increase in H+ production and an equivocal rise in JnsK. Increasing the nutrient potassium concentration (Kn) to 8.5 mEq/l. in the presence of histamine induced a depression in PD, although the rate of acid secretion was unchanged. Hydrogen ion secretion decreased when the nutrient potassium concentration was decreased to 1 mEq/l. despite the continued presence of histamine. The response of JnsK to alterations in nutrient potassium concentration was unaffected by the presence of either histamine or thiocyanate. Thiocyanate produced almost complete inhibition of H+ secretion and a rise in PD. Raising the nutrient potassium concentration in the presence of thiocyanate produced a prompt and sustained fall in PD, followed by a transient rise when Kn was lowered. Alterations of the nutrient potassium concentration in the presence of thiocyanate had no effect on the rate of acidification. The data indicate that under certain circumstances PD and H+ secretion can be uncoupled and that the inverse relationship between Kn and PD is substantially independent of the rate of H+ secretion.

Effect of potassium on ion transport and bioelectric potentials of frog gastric mucosa.

Ion transport of the isolated frog gastric mucosa was studied in vitro by the chamber method. The effects of modifications in the concentrations of potassium in nutrient (Kn+) and in secretory (Ks+) solutions on net potassium flux from nutrient to secretory phases (JnsKK+) on the rate of H+ production and on the transmucosal potential difference (PD) was studied in this system. Both the rate of H+ secretion and JnsKK+ increased when Kn+ was raised and decreased when Kn+ was lowered. Reduction of Kn+ to zero produced a striking depression of H+ secretion, which was reversed by adding K+ to the nutrient phase. Serial differences in H+ production (ΔH+) were approximately proportionate to the serial changes in Kn+. Transmucosal PD varied inversely with Kn+. Modification in Ks+ failed to alter H+ production or PD, although JKnsKns+ was decreased by raising Ks+.