Interaction of calmodulin inhibitors and protein kinase C inhibitors with voltage-dependent calcium channels.

We compared the relative abilities of a series of calmodulin inhibitors and protein kinase C inhibitors to influence 45Ca2+ influx through voltage-dependent Ca2+ channels in PC12, a clonal neural cell line. K+-depolarization-dependent 45Ca2+ uptake was reduced by the calmodulin inhibitors calmidazolium, trifluoperazine, W-7, W-13, and W-5 at concentrations comparable to those that affect calmodulin, while the protein kinase C inhibitors polymyxin B and H-7 were weak or ineffective. The Ca2+ channel antagonist properties of calmodulin inhibitors should be considered in interpreting their effects on Ca2+-dependent cellular events.