Cyclic AMP and intracellular ionic activities innecturus gallbladder

Summary

Open-tip and liquid ion-exchanger microelectrodes were used to study the effects of cAMP (6mm, added to the serosal medium) on apical membrane potential (E _m ) and intracellular sodium, potassium, and chloride activities (a ⁱ_Na ,a ⁱ_K ,a ⁱ_Cl ) inNecturus gallbladder under open-circuit conditions. Transepithelial potential difference (E _Tr ) was also measured. In the presence of cAMP,a ⁱ_Cl fell from about 1.5 times its equilibrium value to a level that corresponded to electrochemical equilibrium across the apical and basolateral cell membranes. Under these conditionsa ⁱ_Na decreased anda ⁱ_K increased,E _m was unchanged andE _Tr increased from virtually zero to a small but significant serosal positive value. The cAMP-induced increase ina ⁱ_K was abolished when Cl⁻-free incubation media were used. Addition of the Ca⁺⁺-ionophore A23187 (0.5 ⧎g/ml) to the serosal medium had no effect onE _m ,E _Tr , ora ⁱ_Cl . When A23187 was added to the mucosal medium,E _m and the basolateral membrane potential hyperpolarized by about 20 mV and an increase in the outwardly directed electrochemical driving force for Cl⁻ was observed. These results indicate that cAMP inhibits coupled transapical Na−Cl entry into epithelial cells ofNecturus gallbladder and suggest that this inhibition may not be mediated by an increase in intracellular Ca⁺⁺ concentration.