Non-genomic regulation of intermediate conductance potassium channels by aldosterone in human colonic crypt cells.

Abstract

Aldosterone has a rapid, non-genomic, inhibitory effect on macroscopic basolateral K(+) conductance in the human colon, reducing its capacity for Cl(-) secretion. The molecular identity of the K(+) channels constituting this aldosterone inhibitable K(+) conductance is unclear. To characterise the K(+) channel inhibited by aldosterone present in the basolateral membrane of human colonic crypt cells. Crypts were isolated from biopsies of healthy sigmoid colon obtained during colonoscopy. The effect of aldosterone on basolateral K(+) channels, and the possible involvement of Na(+):H(+) exchange, were studied by patch clamp techniques. Total RNA from isolated crypts was subjected to reverse transcriptase-polymerase chain reaction (RT-PCR) using primers specific to intermediate conductance K(+) channels (KCNN4) previously identified in other human tissues. In cell attached patches, 1 nmol/l aldosterone significantly decreased the activity of intermediate conductance (27 pS) K(+) channels by 31%, 53%, and 54% after 1, 5 and 10, minutes, respectively. Increasing aldosterone concentration to 10 nmol/l produced a further 56% decrease in channel activity after five minutes. Aldosterone 1-10 nmol/l had no effect on channel activity in the presence of 20 micro mol/l ethylisopropylamiloride, an inhibitor of Na(+):H(+) exchange. RT-PCR identified KCNN4 mRNA, which is likely to encode the 27 pS K(+) channel inhibited by aldosterone. Intermediate conductance K(+) channels (KCNN4) present in the basolateral membranes of human colonic crypt cells are a target for the non-genomic inhibitory effect of aldosterone, which involves stimulation of Na(+):H(+) exchange, thereby reducing the capacity of the colon for Cl(-) secretion.