Protein kinase C-independent inhibition of arterial smooth muscle K+channels by a diacylglycerol analogue

Abstract

Analogues of the endogenous diacylglycerols have been used extensively as pharmacological activators of protein kinase C (PKC). Several reports show that some of these compounds have additional effects that are independent of PKC activation, including direct block of K(+) and Ca(2+) channels. We investigated whether dioctanoyl-sn-glycerol (DiC8), a commonly used diacylglycerol analogue, blocks K(+) currents of rat mesenteric arterial smooth muscle in a PKC-independent manner. Conventional whole-cell and inside-out patch clamp was used to measure the inhibition of K(+) currents of rat isolated mesenteric smooth muscle cells by DiC8 in the absence and presence of PKC inhibitor peptide. Mesenteric artery smooth muscle K(v) currents inactivated very slowly with a time constant of about 2 s following pulses from -65 to +40 mV. Application of 1 µM DiC8 produced an approximate 40-fold increase in the apparent rate of inactivation. Pretreatment of the cells with PKC inhibitor peptide had a minimal effect on the action of DiC8, and substantial inactivation still occurred, indicating that this effect was mainly independent of PKC. We also found that DiC8 blocked BK and K(ATP) currents, and again a significant proportion of these blocks occurred independently of PKC activation. These results show that DiC8 has a direct effect on arterial smooth muscle K(+) channels, and this precludes its use as a PKC activator when investigating PKC-mediated effects on vascular K(+) channels.