EFFECTS OF HALOTHANE, ISOFLURANE AND SEVOFLURANE ON CALCIUM-RELATED CONTRACTION IN PORCINE CORONARY-ARTERIES

Background: Volatile anaesthetics have a direct inhibitory effect upon epicardial coronary arterial smooth muscles (1-4). The site and mode of their action at the cellular level need to be clarified, which was the purpose of our study. The present investigation attempted to answe r the question in what way volatile anaesthetics influence Ca2+-relate d contraction in isolated porcine epicardial coronary to understand th eir intracellular mechanism. Methods: Isolated helical strips of porci ne epicardial coronary artery without endothelium were suspended for i sotonic contraction recordings in Krebs-Ringer's solution. 9.4x10(-2) M K+, 2.5x10(-3) M Ca2+-induced shortening of the strips was regarded as the reference value (100%). After incubation in Ca2+-free solution with 10(-3) M ethlene glycol bis (beta-aminoethyl ether)-N,N-tetraacet ic acid (EGTA) for 60 minutes, the muscle strips were exposed to incre asing Ca2+ concentrations (10(-4)-10(-2)) either in the presence or ab sence of 1.5 or 2.5 minimum alveolar concentration (MAC) halothane, is oflurane or sevoflurane, with 9.4x10(-2) M K+ bath solution. Results: All three drug groups produced apparent biphasic effects with a cumula tive increase of Ca2+ concentration compared with control groups. An i nitial increase at low Ca2+ concentration was followed by a decrease o f Ca2+-activated contractions. Isoflurane affected Ca2+-induced contra ction significantly more than halothane and sevoflurane. Conclusions: The results imply that volatile anaesthetics influence Ca2+-dependent activity of coronary smooth muscle by complex mechanisms, which involv e promotion of intracellular Ca2+ release and other mechanisms that al ter sensitivity to calcium.