Hormonal modulations of calcium channel activity

Hormones and neurotransmitters which modulate the membraneous influx of calcium into the cytoplasm interact with heptahelical receptors coupling to heterotrimeric G-proteins. Whereas early studies on cardiomyocytes demonstrated the involvement of a cAMP (cyclic adenosine monophosphate)-stimulated phosphorylation in the regulation of calcium channels, there is growing evidence for a direct coupling of G-proteins to these channels. Various approaches led to the identification of the subtypes of G-protein involved in these signal transduction processes. Intranuclear injections of antisense oligonucleotides hybridizing to the mRNA of G-protein subunits and, thereby, blocking the expression of these proteins showed a high specificity of the involved G-proteins, suggesting a selective processing of signals from receptors through G-proteins. Whereas hormonal inhibitions of voltage-dependent calcium channels are mediated by G-proteins of the G0-family, hormonal stimulations involve G-protein of the G1-family and protein kinase C.