Activity of the basolateral K⁺ channels is coupled to the Na⁺-K⁺-ATPase in the cortical collecting duct

Microelectrode and patch-clamp techniques were used in the isolated cortical collecting duct to study the effects of stimulating Na ⁺-K⁺-ATPase by raising bath K⁺ (Fujii Y and Katz AI. Am J Physiol Renal Fluid Electrolyte Physiol 257: F595-F601, 1989 and Muto S, Asano Y, Seldin D, and Giebisch. Am J Physiol Renal Physiol 276: F143-F158, 1999) on the transepithelial (V_T) and basolateral membrane (V_B) voltages and basolateral K⁺ channel activity. Increasing bath K⁺ from 2.5 to 8.5 mM resulted in an initial hyperpolarization of both V_T and V_B followed by a delayed depolarization. The effects of raising bath K⁺ on V _T and V_B were attenuated by decreasing luminal Na ⁺ from 146.8 to 14.0 mM and were abolished by removal of luminal Na⁺, whereas those were magnified in desoxycorticosterone acetate (DOCA)-treated rabbits. Increasing bath K⁺ also led to a significant reduction of the intracellular Na⁺ and Ca²⁺ concentrations. The transepithelial conductance (G_T) or fractional apical membrane resistance (fR_A) were unaltered during the initial hyperpolarization phase, whereas, in the late depolarization phase, there were an increase in G_T and a decrease in fR_A, both of which were attenuated in the presence of low luminal Na⁺ (14.0 mM). In tubules from DOCA-treated animals, bath Ba²⁺ not only caused a significantly larger initial hyperpolarization of V_T and V _B but also blunted the late depolarization by high bath K ⁺. Nω-nitro-L-arginine methyl ester (L-NAME) partially mimicked the effect of Ba²⁺ and decreased the amplitude of the late depolarization. Patch-clamp experiments showed that raising bath K⁺ from 2.5 to 8.5 mM resulted in an increased activity of the basolateral K ⁺ channel, which was absent in the presence of L-NAME. We conclude that stimulation of Na⁺-K⁺-ATPase increases the basolateral K⁺ conductance and that this effect involves suppression of nitric oxide-dependent inhibition of K⁺ channels.