IP3-induced Ca2+ release in A7r5 vascular smooth-muscle cells represents a partial emptying of the stores and not an all-or-none Ca2+ release of separate quanta |
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Authors: | L. Missiaen H. Sipma J. B. Parys P. De Smet G. Callewaert E. Hill T. V. McCarthy H. De Smedt |
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Affiliation: | (1) Laboratorium voor Fysiologie, K.U. Leuven Campus Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium e-mail: Ludwig.Missiaen@med.kuleuven.ac.be Tel.: +32-16-345720, Fax: +32-16-345991, BE;(2) Department of Biochemistry, University College Cork, Lee Maltings, Prospect Row, Cork, Ireland, IE |
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Abstract: | There is still no agreement on the mechanism of the intracellular action of low concentrations of inositol 1,4,5-trisphosphate (IP3). Intracellular Ca2+ stores may transiently release some Ca2+ before they become insensitive to IP3. Alternatively, stores with a low IP3 threshold may lose all their Ca2+ and the others none. We now report that the IP3 threshold was not correlated with the extent of Ca2+ release in permeabilized A7r5 smooth-muscle cells. In contrast, the maximum rate of release, which was changed either by varying the level of IP3 receptor (IP3R) activation, or by changing the concentration of IP3R at a constant level of IP3R activation, was directly related to the extent of Ca2+ release. We conclude that IP3-induced Ca2+ release reflects partial emptying of the stores and not all-or-none Ca2+ release of separate quanta. Received: 22 October 1998 / Received after revision: 15 December 1998 / Accepted: 11 January 1999 |
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Keywords: | Ca2+ stores IP3 receptor Intracellular Ca2+ release |
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