title: Alpha 1-adrenoceptor subtypes linked to different mechanisms for increasing intracellular Ca2+ in smooth muscle.
abstract: Receptor-mediated increases in intracellular Ca2+ levels can be caused by release from intracellular organelles and/or influx from the extracellular fluid. Noradrenaline (NA) released from sympathetic nerves acts on alpha 1-adrenoceptors to increase cytosolic Ca2+ and promote smooth muscle contraction. In many cells activation of alpha 1-adrenoceptors causes formation of inositol 1,4,5-trisphosphate which promotes Ca2+ release from intracellular stores. The mechanism by which receptor activation opens cell surface Ca2+ channels is not known, although in some cases it may be secondary to formation of inositol phosphates or release of stored intracellular Ca2+ (ref. 3). However, alpha 1-adrenoceptors have recently been shown to have different pharmacological properties in different tissues, and it has been proposed that different alpha 1-adrenoceptor subtypes may control mobilization of intracellular Ca2+ and gating of extracellular Ca2+ influx. We here report evidence for two subtypes of alpha 1-adrenoceptors which cause contractile responses through different molecular mechanisms. One subtype stimulates inositol phosphate (InsP) formation and causes contractions which are independent of extracellular Ca2+, and the other does not stimulate inositol phosphate formation and causes contractions which require the influx of extracellular Ca2+ through dihydropyridine-sensitive channels. These results suggest that neurotransmitters and hormones may control Ca2+ release from intracellular stores and influx through voltage-gated membrane channels through distinct receptor subtypes.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004095:Dihydropyridines; D006624:Hippocampus / Q000502:physiology; D007295:Inositol Phosphates / Q000096:biosynthesis; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D008099:Liver / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism*; D010627:Phenethylamines / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013154:Spleen / Q000502:physiology; D044024:Tetralones; D014649:Vas Deferens / Q000502:physiology
chemical_list: D000317:Adrenergic alpha-Antagonists; D004095:Dihydropyridines; D007295:Inositol Phosphates; D007473:Ion Channels; D010627:Phenethylamines; D011725:Pyridines; D011942:Receptors, Adrenergic, alpha; D044024:Tetralones; C010652:BE 2254; C038806:1,4-dihydropyridine; D002118:Calcium