Regulation of Na channels in the rat cortical collecting tubule: Effects of cAMP and methyl donors

The whole cell patch-clamp technique was used to investigate the interactions of the amiloride-sensitive Na channel of the rat cortical collecting tubule (CCT) with adenosine 3',5'-cyclic monophosphate (cAMP) and with methyl donors. The amiloride-sensitive whole cell current (I-Na) was measured in principal cells of dissected, split-open tubules from rats maintained either on a control diet or on a low-Na diet to increase endogenous aldosterone secretion. With Na-depleted animals, IN, was highest immediately after rupture of the membrane patch and averaged 325 pA at a membrane potential of -60 mV. I-Na declined over 15 min to similar to 35% of the initial value. With 8-(4-chlorophenylthio)-cAMP in the pipette, IN, increased within 5 min of membrane rupture and was maintained for 15 min at levels three- to fourfold higher than the corresponding control values. With Na-replete animals, I-Na was undetectable (<10 pA) without cAMP. With cAMP in the pipette, I-Na averaged 40 pA. In cell-attached patches on tubules from Na-replete rats exposed to cAMP, single Na channels mere observed with conductive and kinetic properties similar to those from Na-depleted rats but at lower density. Inclusion of the methyl donor S-adenosyl methionine to the pipette solution did not increase I-Na in CCTs from Na-replete rats, either in the presence or absence of cAMP. We methylation inhibitor S-adenosyl homocysteine did not affect I-Na in CCT from Na-depleted animals.