Activation of calcium sparks by angiotensin II in vascular myocytes.
Contraction in smooth muscle is triggered by an increase in cytoplasmic free calcium ([Ca2+]i) which depends on both Ca2+ influx through L-type Ca2+ channels and Ca2+ release from the sarcoplasmic reticulum (SR). Two mechanisms have been shown to be involved in SR Ca2+ release, one is stimulated by Ca2+ and involved ryanodine-sensitive Ca2+-release channels; the other is stimulated by an increase in inositol 1,4,5-trisphosphate (InsP3) generation induced by various mediators and involved InsP3-sensitive Ca2+ release channels. Here, we examined the effects of angiotensin II on [Ca2+]i in single rat portal vein myocytes using both the whole cell patch-clamp method and a laser scanning confocal microscope. Elementary Ca2+ release events (Ca2+ sparks) were obtained spontaneously or in response to L-type Ca2+ channel current activation, and resulted from activation of ryanodine-sensitive Ca2+-release channels in the SR. We show that angiotensin AT1 receptors stimulate Ca2+ sparks through activation of L-type Ca2+ channels without involving InsP3-induced Ca2+ release. This novel transduction pathway may be a common mechanism for vasoconstrictors which do not stimulate generation of chemical second messengers.
Arnaudeau
S
S
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, CNRS ESA 5017, Université de Bordeaux II, France.
Macrez-Leprêtre
N
N
Mironneau
J
J
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D004095:Dihydropyridines / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011169:Portal Vein; D051381:Rats; D017208:Rats, Wistar; D011945:Receptors, Angiotensin / Q000502:physiology*
D015220:Calcium Channels; D004095:Dihydropyridines; D011945:Receptors, Angiotensin; D000804:Angiotensin II; C053783:oxodipine; D002118:Calcium