Inositol 1,4,5-trisphosphate-induced Ca2+ release is regulated by cytosolic Ca2+ in intact skeletal muscle |
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Authors: | José R. López Andre Terzic |
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Affiliation: | (1) Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, Caracas, Venezuela, VE;(2) Division of Cardiovascular Diseases, Departments of Internal Medicine and Pharmacology, Mayo Clinic, Mayo Foundation, Rochester, MN-55095, USA, US |
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Abstract: | Microinjection of inositol 1,4,5-trisphosphate (InsP 3) into intact skeletal muscle fibers isolated from frogs (Rana temporaria) increased resting cytosolic Ca2+ concentration ([Ca2+]i) as measured by double-barreled Ca2+-selective microelectrodes. In contrast, microinjection of inositol 1-phosphate, inositol 1,4-biphosphate, and inositol 1,4,5,6-tetrakisphosphate did not induce changes in [Ca2+]i. Incubation in low-Ca2+ solution, or in the presence of L-type Ca2+ channel blockers did not affect InsP 3-induced release of cytosolic Ca2+. Neither ruthenium red, a blocker of ryanodine receptor Ca2+-release channels, nor cytosolic Mg2+, a known inhibitor of the Ca2+-induced Ca2+-release process, modified the InsP 3-induced release of cytosolic Ca2+. However, heparin, a blocker of InsP 3 receptors, inhibited InsP 3-induced release of cytosolic Ca2+. Also, pretreatment with dantrolene or azumulene, two inhibitors of cytosolic Ca2+ release, reduced [Ca2+]i, and prevented InsP 3 from inducing release of cytosolic Ca2+. Incubation in caffeine or lengthening of the muscle increased [Ca2+]i and enhanced the ability of InsP 3 to induce release of cytosolic Ca2+. These results indicate that InsP 3, at physiological concentrations, induces Ca2+ release in intact muscle fibers, and suggest that the InsP 3-induced Ca2+ release is regulated by [Ca2+]i. A Ca2+-dependent effect of InsP 3 on cytosolic Ca2+ release could be of importance under physiological or pathophysiological conditions associated with alterations in cytosolic Ca2+ homeostasis. Received: 15 December 1995/Received after revision and accepted: 10 May 1996 |
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Keywords: | Inositol trisphosphate Calcium Skeletal muscle Heparin Ion-selective microelectrodes Dantrolene Ruthenium red |
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