The hypothesis that protein kinase C (PKC) is able to regulate the whole cell Ca-activated K (K_Ca) current independently of PKC effects on local Ca release events was tested using the patch-clamp technique and freshly isolated rat tail artery smooth muscle cells dialyzed with a strongly buffered low-Ca solution. The active diacylglycerol analog 1,2-dioctanoyl-sn-glycerol (DOG) at 10 µM attenuated the current-voltage (I-V) relationship of the K_Ca current significantly and reduced the K_Ca current at +70 mV by 70 ± 4% (n = 14). In contrast, 10 µM DOG after pretreatment of the cells with 1 µM calphostin C or 1 µM PKC inhibitor peptide, selective PKC inhibitors, and 10 µM 1,3-dioctanoyl-sn-glycerol, an inactive diacylglycerol analog, did not significantly alter the K_Ca current. Furthermore, the catalytic subunit of PKC (PKC_C) at 0.1 U/ml attenuated the I-V relationship of the K_Ca current significantly, reduced the K_Ca current at +70 mV by 44 ± 3% (n = 17), and inhibited the activity of single K_Ca channels at 0 mV by 79 ± 9% (n = 6). In contrast, 0.1 U/ml heat-inactivated PKC_C did not significantly alter the K_Ca current or the activity of single K_Ca channels. Thus these results suggest that PKC is able to considerably attenuate the K_Ca current of freshly isolated rat tail artery smooth muscle cells independently of effects of PKC on local Ca release events, most likely by a direct effect on the K_Ca channel.

catalytic subunit of protein kinase C; calcium-activated potassium channel; local calcium release

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