PMA counteracts G protein actions on CaV2.2 channels in rat sympathetic neurons.
Protein kinase C (PKC)-induced phosphorylation and G protein-mediated inhibition of Ca(V)2.2 N-type Ca2+ channels counteract exerting opposing modulatory responses at the channel level. At present, the most striking question remaining is whether prominent enhancement of the Ca2+ current (I(Ca)) observed under PKC activation arises from relief of G-protein tonic inhibition. Here, by using patch-clamp methods in superior cervical ganglion (SCG) neurons of rat, we show the following: First, that PKC activation by phorbol-12-myristate-13-acetate (PMA) not only counteracts mutually with noradrenaline (NA) and GTPgammaS-induced I(Ca) inhibition, but also reverses current inhibition by Gbetagamma subunits over-expression. Second, that PMA increases I(Ca) beyond the enhancement expected by sole removal of the G protein-mediated tonic inhibition. Accordingly, PMA increases conductance through N-type Ca2+ channels, unlike the G protein inhibitor GDPbetaS. Together, our results support that PMA-induced phosphorylation produces changes in I(Ca) that cannot be accounted for by prevention of G protein inhibition. They may have important implications in reinterpretation of existing data with PMA. Furthermore, counteracting modulation of ion channels and reversibility within a short time frame are better support for a dynamic system with short-term adaptive responses.
Díaz-Cárdenas
Alfonso F
AF
Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Av. Universidad 3000, Ciudad Universitaria, Delegación Coyoacán. C.P. 04510, Apdo. Postal 70250, México, DF, México.
Arenas
Isabel
I
García
David E
DE
D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology; D020864:Calcium Channels, N-Type / Q000378:metabolism* / Q000502:physiology; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D018408:Patch-Clamp Techniques; D010641:Phenotype; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D017783:Superior Cervical Ganglion / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013873:Thionucleotides / Q000494:pharmacology
C491367:Cacna1a protein, rat; C503279:Cacna1b protein, rat; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020864:Calcium Channels, N-Type; D013873:Thionucleotides; D006153:Guanosine Diphosphate; C023427:guanosine 5'-O-(2-thiodiphosphate); D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate