Cardiac sarcoplasmic reticulum phosphorylation increases Ca2+ release induced by flash photolysis of nitr-5.
Effects on Ca(2+)-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.
Patel
J R
JR
Department of Physiology, University of Wisconsin Medical School, Madison 53706, USA.
Coronado
R
R
Moss
R L
RL
D000469:Alkaline Phosphatase / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002614:Chelating Agents / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D005260:Female; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D010782:Photolysis; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology; D012503:Saponins / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
D015220:Calcium Channels; D002614:Chelating Agents; D012503:Saponins; C052455:nitr 5; D012433:Ryanodine; D004533:Egtazic Acid; D000242:Cyclic AMP; D000469:Alkaline Phosphatase; D007545:Isoproterenol