Ca2+-calmodulin regulates receptor-operated Ca2+ entry activity of TRPC6 in HEK-293 cells

Mammalian homologues of the Drosophila transient receptor potential channel (TRPC) are involved in Ca2+ entry following agonist stimulation of nonexcitable cells. Seven mammalian TRPCs have been cloned but their mechanisms of activation and/or regulation are still the subject of intense research efforts. It has already been. shown that calmodulin (CaM) can regulate the activity of Drosophila TRP and TRPL and, more recently, CaM has been shown to interact with mammalian TRPCs. In this study, TRPC6 stably transfected into HEK-293 cells was used to investigate the possible influence of CaM on TRPC6-dependent Ca2+ entry Overexpression of TRPC6 in mammalian cells is known to enhance agonist-induced Ca2+ entry, but not thapsigargin-induced Ca2+ entry. Here, we show that CaM inhibitors (calmidazolium and trifluoperazine) abolish receptor-operated Ca2+ entry (ROCE) without affecting thapsigargin-operated Ca2+ entry and that the activity of CaM is dependent on complexation with Ca2+. We also show that Ca2+-CaM binds to TRPC6 and that the binding can be abolished by CaM inhibitors. These results indicate that CaM is involved in the modulation of ROCE. (C) 2002 Elsevier Science Ltd. All rights reserved..