We have used skeletal sarcoplasmic reticulum (SR) as a model to study the effect of anesthetic agents on cardiac SR. We demonstrated the following: (a) heavy SR contains both Ca2+ pump and Ca2+ release channel, while light SR has only Ca2+ pump; (b) anesthetic agents do not inhibit much the Ca2+ pump; (c) anesthetic agents have a large effect on the channel; they increase the permeability of the channel; (d) the increased permeability causes the decrease in the Ca2+ content of SR, which may decrease the muscle contractility (negative inotropism); (e) Ca2+ channel can be isolated and reconstituted into liposome vesicles to demonstrate the Ca2+ release phenomenon; (f) ca2+ single channel conductance of isolated channel protein can be measured; (g) using EPR spin-probe technique, anesthetic agents are shown to increase the fludity of SF membrane; (h) increase of the fluidity is closely correlated with the increase of Ca2+ permeability. Using cardiac SR we also demonstrated that (i) Ca2+ induced Ca2+ release phenomenon of cardiac SR can be studied in vitro; (j) Ca2+ release channel can also be isolated from cardiac SR. We propose to study the following: (a) to elucidate the mechanism of Ca2+ induced Ca2+ release of cardiac SR; (b) to study the effect of anesthetic agents on the Ca2+ release of cardiac SR; (c) to study the similarity and dissimilarity between skeletal and cardiac SR concerning the mechanism of Ca2+ release; (d) to study the effects of anesthetic agents on the membrane fluidity of cardiac SR using spin-probe technique; (e) to study the single channel conductance of channel protein purified from cardiac SR. Through these investigations, we plan to prove the hypothesis that (A) anesthetic agents increase the fluidity of membrane and, as a result, increase the Ca2+ permeability of cardiac SR; (B) the increase of the Ca2+ permeability decreases the Ca2+ content of the SR thereby causing negative inotropism. Our ultimate goal is to elucidate the clinically observed anesthetic-induced inotropism by studying the molecular mechanism of Ca2+ release in cardiac SR.
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