Evidence for capacitative and non-capacitative Ca2+ entry pathways coexist in A10 vascular smooth muscle cells.
It is generally thought that receptor-operated Ca2+ entry is related to store-operated or capacitative Ca2+ entry mechanism. Recent evidence suggests that non-capacitative Ca2+ entry pathways are also involved in receptor activated Ca2+ influx in many different kinds of cells. In this study, we studied whether alpha1-adrenoreceptor (alpha1-AR)-activated Ca2+ entry is coupled to both capacitative and non-capacitative pathways in A10 vascular smooth muscle cells by fura-2 fluorescence probe and conventional whole-cell patch clamp techniques. We found that both thapsigargin (TG) and phenylephrine (Phe) induced transient increase in cytoplasmic Ca2+ concentration ([Ca2+]i) in Ca2+-free medium, and subsequent addition of Ca2+ evoked a sustained [Ca2+]i rise. When the membrane potential was held at -60 mV, both TG and Phe activated inward currents, which were inhibited by GdCl3(Gd3+), 0Na+/0Ca2+ solution and 1-{beta[3-(4-mehtoxyphenyl)propoxy]-4-methoxypheneth-yl}-1H- imidazole hydro-chloride (SK&F96365), but not by nifedipine. When Ca2+ store was depleted by TG in Ca2+-free solution, Phe failed to further evoke [Ca2+]i rise. However, when capacitative Ca2+ entry was activated by TG in the medium containing Ca2+, 10 microM Phe further increased [Ca2+]i. At the same concentration, TG activated an inward cation current, subsequent addition of Phe also further induced an inward cation current. Furthermore, the amplitudes of [Ca2+]i increase and current density induced by Phe in the presence of TG were less than that induced by Phe alone. Our results suggest that both capacitative and non-capacitative Ca2+ entry pathways are involved in Ca2+ influx induced by activation of alpha1-AR in A10 vascular smooth muscle cells.
Zhou
Jia-Guo
JG
Department of Pharmacology, Cardiac and Cerebral Vascular Research Center, Zhongshan Medical College, Sun Yat-Sen University 74 Zhongshan 2 Rd Guangzhou, Guangdong, 510089, China.
Qiu
Qin-Ying
QY
Zhang
Zheng
Z
Liu
Yu-Jie
YJ
Guan
Yong-Yuan
YY
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D005456:Fluorescent Dyes / Q000032:analysis; D016257:Fura-2 / Q000032:analysis; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D050052:TRPC Cation Channels / Q000187:drug effects / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005456:Fluorescent Dyes; D050052:TRPC Cation Channels; D010656:Phenylephrine; D019284:Thapsigargin; D002118:Calcium; D016257:Fura-2