The regulation of the cytoplasmic free Ca2+ concentration in aortic smooth muscle cells (A7r5 line) after stimulation by vasopressin and bombesin.
The characteristics of intracellular Ca2+ transient induced by vasopressin and bombesin in aortic smooth muscle cells were studied using flow cytometric analysis of indo-1 loaded cells. The two hormones induced a rapid and transient rise in [Ca2+]i. This Ca2+ transient was independent of the presence of extracellular Ca2+. Addition of bombesin to cells that have already been stimulated by vasopressin (or conversely the addition of vasopressin to bombesin-stimulated cells) results in a second Ca2+ transient that has a smaller amplitude. This transient is the same when the external Ca2+ concentration is lowered from 1.8 mM to 50 nM, suggesting that the agonist-sensitive pool reloaded using the Ca2+ that has been previously released into the cytoplasm. Intracellular Ca2+ pools that have been depleted by a prolonged incubation of the cells in a low Ca2+ medium can be refilled by shifting cells to a high Ca2+ medium. The reloading was analyzed in detail and found to be a slow process. It is hardly affected by Ni2+ or by (-)D888, a potent inhibitor of the voltage-dependent Ca2+ channels. It is accelerated when Ca2+ uptake by the Na+/Ca2+ exchange system is stimulated. The results suggest that Ca2+ homeostasis in aortic smooth muscle cells is achieved using mechanisms that are distinct from those operating in various acini and in striated muscles.
Vigne
P
P
Centre de Biochimie, Centre National de la Recherche Scientifique, Nice, France.
Breittmayer
J P
JP
Lazdunski
M
M
Frelin
C
C
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D001839:Bombesin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D005434:Flow Cytometry; D007295:Inositol Phosphates / Q000096:biosynthesis; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D013268:Stimulation, Chemical; D014667:Vasopressins / Q000494:pharmacology*
D007295:Inositol Phosphates; D014667:Vasopressins; D001839:Bombesin; D002118:Calcium