RESUMO
<p><b>AIM</b>The characteristics of ryanodine receptor in rat cardiac sarcoplasmic reticulum (SR) and nuclear envelope (NE) were studied.</p><p><b>METHODS</b>Velocity and isopyknic gradient centrifugation was employed to fractionate rat SR and NE. Ryanodine receptor was assayed with [3H] ryanodine saturate binding to the preparations.</p><p><b>RESULTS</b>The maximal binding (Bmax) and dissociating constant (Kd) of ryanodine receptor in rat cardiac NE were, 1.7% and 60% of those in SR respectively. Phosphorylation in vitro by PKA and PKC increased Bmax of the receptors in SR by 372% and 121%, and augmented those in NE by 221% and 306%, without any effects on Kd.</p><p><b>CONCLUSION</b>Ryanodine receptors were present in rat myocardial NE, with lower density and higher affinity than those located in SR, which can be activated by PKA and PKC.</p>
