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Circulation Research. 1995;77:943-949

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(Circulation Research. 1995;77:943.)
© 1995 American Heart Association, Inc.


Articles

Cardiac Sarcoplasmic Reticulum Phosphorylation Increases Ca2+ Release Induced by Flash Photolysis of Nitr-5

Jitandrakumar R. Patel, Roberto Coronado, Richard L. Moss

From the Department of Physiology, University of Wisconsin Medical School, Madison.

Correspondence to Dr Richard L. Moss, Department of Physiology, University of Wisconsin Medical School, 1300 University Ave, Madison, WI 53706.

Abstract Effects on Ca2+-induced Ca2+ release due to phosphorylation of sarcoplasmic reticulum (SR) proteins were investigated in isoproterenol-treated saponin-permeabilized trabeculae from rat ventricles. In these experiments, Ca2+ release from the SR was induced by a rapid change in concentration of free Ca2+ (ie, trigger Ca2+) achieved by flash photolysis of nitr-5, and the amount of Ca2+ released was assessed by measuring isometric tension. Ca2+ uptake by the SR was more rapid, and the amount of Ca2+ released by a given concentration of trigger Ca2+ was greater in isoproterenol-treated trabeculae compared with control trabeculae. However, under the same conditions of Ca2+ loading, the amplitudes of caffeine-elicited tension transients in control trabeculae were similar to those in isoproterenol-treated trabeculae, suggesting that the Ca2+ available for release was similar in the two cases. Control experiments showed that there were no significant differences in Ca2+ sensitivity of tension between isoproterenol-treated and control trabeculae. Also, application of alkaline phosphatase to trabeculae that had previously been treated with isoproterenol returned SR Ca2+ release to control levels. We conclude that the greater release of Ca2+ in isoproterenol-treated trabeculae in response to a given concentration of trigger Ca2+ is due to phosphorylation of SR proteins, most likely the Ca2+ release channel.


Key Words: ventricular trabeculae • sarcoplasmic reticulum • Ca2+-induced Ca2+ release • flash photolysis • phosphorylation