Various mechanisms have been identified by which hormones and neurotransmitters interacting with seven transmembrane alpha-helical spanning segments receptors modulate the activity of ion channels. All of the mechanisms involve heterotrimeric G-proteins; the best documented are hormonal modulations of voltage-dependent Ca2+ channels in cardiac, neuronal and endocrine cells. Recent studies using antisense oligonucleotide probes allow the exact identification of the G-proteins involved in these signal transduction pathways.