Activation of KCa channels in airway smooth muscle cells by endogenous protein kinase A
Wang, Z.W.; Kotlikoff, M.I.
American Journal of Physiology 271(1 Pt 1): L100-L105
1996
ISSN/ISBN: 0002-9513 PMID: 8760138 Document Number: 464172
The regulation of calcium-activated potassium (K-Ca) channels by endogenous protein kinase A (PKA) was examined in inside-out patches from equine tracheal myocytes. In the absence of exogenous protein kinases, ATP (500 mu-M) significantly augmented K-Ca channel activity when applied to the cytosolic patch surface (open-state probability (nP-o, mean +- SE) increased from 0.010 +- 0.001 to 0.034 +- 0.005 (n = 24)). The stimulatory effect of ATP was mimicked by ATP-gamma-S but not by AMP-PNP. Rather, AMP-PNP significantly inhibited channel activity. The PKA inhibitory peptide (PKI) significantly reduced nP-o and prevented the augmenting effect of subsequent ATP. Ht 31, an inhibitory peptide for A-kinase-anchoring proteins (AKAP), but not its proline-substituted mutant, also blocked the stimulatory effect of ATP. These results suggest that 1) ATP augments K-Ca channel activity through phosphorylation; 2) the phosphorylation is catalyzed by endogenous PKA; 3) anchoring via AKAP is required to maintain association of PKA with the membrane; and 4) in a newly obtained patch, some of the K-Ca channels are probably already in a phosphorylated state.