Role of protein kinase C in aldosterone-induced non-genomic inhibition of basolateral potassium channels in human colonic crypts

Aldosterone produces rapid, non-genomic, inhibition of basolateral intermediate conductance K+ (IKCa) channels in human colonic crypt cells but the intracellular second messengers involved are unclear. We therefore evaluated the role of protein kinase C (PKC) in aldosterone's non-genomic inhibitory effect on basolateral IKCa channels in crypt cells from normal human sigmoid colon. Patch clamp studies revealed that in cell-attached patches, IKCa channel activity decreased progressively to 38 ± 8% (P < 0.001) of the basal value 10 min after the addition of 1 nmol/L aldosterone, and decreased further to 23 ± 6% (P < 0.02) of the basal value 5 min after increasing the aldosterone concentration to 10 nmol/L. Pre-incubation of crypts with 1 μmol/L chelerythrine chloride or 1 μmol/L Gö 6976 (PKC inhibitors) prevented the inhibitory effect of aldosterone. Conversely, channel activity decreased to 60 ± 9% (P < 0.02) of the basal value 10 min after the addition of 500 nmol/L PMA (a PKC activator), whereas 4α-PMA (an inactive ester) had no effect. When aldosterone (10 nmol/L) and PMA were added together, IKCa channel activity was inhibited to the same extent as with aldosterone alone. These results indicate that aldosterone's non-genomic inhibitory effect on the macroscopic basolateral K+ conductance in human colonic crypts reflects PKC-mediated inhibition of IKCa channels.