Modification mechanisms of single ionic channel currents from cardiac sarcoplasmic reticulum and mitochondria by physiologically active substances.

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Effects of physiologically active substances on the single channel molecules from cardiac sarcoplasmic reticulum and mitochondria were examined by using the planar lipid bilayr, the hot ligand binding, and the ^<45>Ca^<2+> efflux methods. Systematic screening works were performed in great many kinds of substances and ionic channels. It is the most important findings that cytoplasmic application of arachidonic acids and polyamines causes a potent functional modulation in the ryanodine receptor channels. We have already published a paper related to the activated mechanism by the arachidonic acid and analogs, the summary of which is shown below. Also, we have submitted a paper related to the inhibited mechanism by the polyamines to some journal. The latter paper is now in Revise.ArticleA.UEHARA,M.YASUKOCHI AND I.IMANAGA.Modulation of Ryanodine Binding to the Cardiac Ca^<2+> Release Channel by Arachidonic Acid. Journal of Molecular and Cellular Cardiology (1996) 28,43-51. Effects of arachidonic acid (AA) on the Ca^<2+> 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 K_<hatf> values of the dose-response curve were 12 and 97 muM in the JSR membrane vesicles and the solubilized proteins, respectively. Moreover, Michaelis, Scatchard and Lineweaver-Burk analyzes were performed to evaluate K_<d+> B_<max> and K_d/B_<max> values. During exposure to AA,the K_d value increased while the B_<max> value decreased. These results suggest that AA directly modifies the structure of the ryanodine binding site.(c) 1996 Academic Press Limited