Modulation of ryanodine binding to the cardiac Ca2+ release channel by arachidonic acid

Effects of arachidonic acid (AA) on the Ca2+ release channels in cardiac sarcoplasmic reticulum were examined by the 3H-ryanodine binding method. The samples used were membrane vesicles of junction sarcoplasmic reticulum (JSR) and solubilized ryanodine receptor proteins. AA inhibited the amount of hot ryanodine bound to its receptor in both types of samples and this inhibitory effect was dose-dependent. The Khalf values of the dose-response curve were 12 and 97 microM in the JSR membrane vesicles and the solubilized proteins, respectively. Moreover, Michaelis, Scatchard and Lineweaver-Burk analyses were performed to evaluate Kd, Bmax and Kd/Bmax values. During exposure to AA, the Kd value increased while the Bmax value decreased. These results suggest that AA directly modifies the structure of the ryanodine binding site.