Inositol-1,4,5-trisphosphate releases calcium from skinned cultured smooth muscle cells.
ABSTRACT We examined the effects of inositol-1,4,5-trisphosphate on 45Ca uptake and 45Ca efflux in the saponin skinned primary cultured rat aortic smooth muscle cells. 10 microM inositol-1,4,5-trisphosphate induced a rapid (half time less than 10 sec) and large quantity of Ca release in both 45Ca uptake and 45Ca efflux in the skinned cells preloaded with 1 microM free Ca. Dose response curves showed that 100 microM inositol-1,4,5-trisphosphate produced a maximal Ca release of 97.3% of the MgATP dependent 45Ca uptake or 289 mumoles/liter cells, which was much greater than the maximal caffeine induced Ca release and would be sufficient to produce maximal tension.
[Show abstract] [Hide abstract]
ABSTRACT: In Ca 2+ -free EGTA-containing solution serotonin induced a transient contraction of rabbit pulmonary artery smooth muscle which decayed to nearly steady-state level accounted for 17.7 +/- 1.6% of original contraction in Krebs solution. Both phasic and tonic components of this contraction were effectively inhibited by verapamil and Cd 2+ . Caffeine induced no contraction of muscle strips if it was applied after withdrawal of serotonin. But when the sequence of these drugs application was reversed, serotonin still evoked contraction with reduced phasic component. The results obtained in these experiments suggest, that serotonin-induced contraction of pulmonary artery smooth muscle is partly (less than 20%) due to mobilization of bound calcium from at least two stores located on the opposite sides of the cell membrane. Calcium released from external store site enters the cell via receptor-operated calcium channelsBulletin of Experimental Biology and Medicine 09/1988; 106(3):1211-1214. DOI:10.1007/BF00834475 · 0.37 Impact Factor
01/2010; 2(1):1-62. DOI:10.4199/C00012ED1V01Y201005ISP007
[Show abstract] [Hide abstract]
ABSTRACT: A method for saponin skinning of primary cultured rat aortic smooth muscle cells was established . The Saponin-treated cells could be stained with trypan blueand incorporated more "Ca" than the nontreated cells under the same conditions . At low free Ca" concentration, >85% of"Ca" uptake into the skinned cells was dependent on the extracellularly supplied MgATP. In the intact cells, both caffeine and norepinephrine increased"Ca" efflux . In the skinned cells, caffeine increased "'Ca" efflux, whereas norepinephrine did not. The caffeine-releasable"Ca" uptake fraction in theskinned cellsappeared at 3 x 10'M Ca", increased gradually with the increase in free Ca" concen- tration, and reached a plateau at 1 x 10-5MCa". The "Ca' uptake fraction, which was significantly suppressed by sodium azide, appeared at 1 x 10-5 M Ca" and increased monotonically with increasing free Ca"concentration. The results suggest that the caffeine-sensitive Ca' store, presumably the sarco- plasmic reticulum, plays a physiological role by releasing Ca' in response to norepinephrine or caffeine and by buffering excessive Cat+. The"Ca" uptake by mitochondria appears too insensitive to be important under physiological conditions .