Potential difference responses to nutrient K +, Na + and Cl − changes with varying nutrient HCO 3− in resting frog stomach

Abstract

The effects of changes in nutrient concentrations of K +, Na + and Cl − on the transmucosal potential difference (PD) and resistance were compared for 25 and 5 mM nutrient HCO 3 − in resting fundus. With 25 mM HCO 3 −, increase of K + from 4 to 40 mM, decrease of Na + from 100 to 10 mM and decrease of Cl − from 81 to 8.1 mM gave, 10 min after the change, ΔPD values of −23.2, −15.1 and −21.3 mV, respectively. With 5 mM HCO 3 −, the same changes in nutrient ion concentration gave ΔPD values of −11.9, −9.4 and −10.0 mV, respectively. From these results, in going from 25 to 5 mM HCO 3 − it follows that the resistances of the ionic pathways for K +, Na + and Cl − increased. The anomalous PD response following the increase in nutrient K + from 4 to 40 mM with 5 mM nutrient HCO 3 − gave further evidence that the resistance of the simple K + conductance pathway increased prior to the increase to 40 mM K +. The fact that 2 mM Ba 2+ in the 25 mM HCO 3 − nutrient gave a smaller increase in resistance, compared to the decrease in nutrient HCO 3 − from 25 to 5 mM, supported the inference that resistances of ion pathways other than that of the K + pathway increased.