DIFFERENTIAL-EFFECTS OF HALOTHANE AND ISOFLURANE ON CONTRACTILE-FORCEAND CALCIUM TRANSIENTS IN CARDIAC PURKINJE-FIBERS

Background: Halothane and isoflurane have been shown to differentially effect mechanisms of contraction in working myocardial fibers. The ai m of this study was to compare effects of halothane and isoflurane on contractile force (CF) and Ca2+ transients in canine cardiac Purkinje fiber preparations. Methods: Fiber preparations (n = 29) were superfus ed with Krebs-Ringer solution and stimulated at 40-60 pulses/min at 30 degrees C in the absence and presence of 0.55% and 1.01% isoflurane o r 0.27% and 0.78% halothane. Isometric tension (CE), and intracellular Ca2+ transients (luminescence, L) were measured after microinjecting the Ca2+ sensitive photoprotein aequorin into Purkinje fibers. Peak CF and peak L, rate of rise (slope) of CF and L, time to attain peak CF and L, and duration of CF and L at half-peak CF and L, were measured a t 5 mM extracellular CaCl2. Changes in peak CF and peak L also were me asured during incremental increases in CaCl2 from 3.6 to 9.0 mM. Resul ts: Both anesthetics depressed peak CF and peak L and the rate of incr ease in peak CF and L in a concentration-dependent fashion, and effect s of halothane were greater than those of isoflurane. Time to attain p eak L and duration of L at half-peak L was decreased or unchanged by i soflurane and was increased by halothane, whereas time to attain peak CF and duration of CF at half-peak CF was shortened by both. The chang e in peak CF response as a function of the change in peak L with incre asing extracellular CaCl2 was attenuated similarly by both halothane a nd isoflurane. Conclusions: Halothane depresses peak CF and Ca2+ trans ients and prolongs Ca2+ transients more than does isoflurane at equiva lent minimum alveolar concentration in Purkinje fibers. This suggests Ca2+ concentration Is differentially altered by anesthetics in this ti ssue. Peak CF at equivalent peak Ca2+ transients, however, appears to be attenuated similarly by both anesthetics. These differences in anes thetic effect are qualitatively similar to those found in cardiac tiss ue of other species. These findings add to our understanding of effect s of volatile anesthetics on contractile properties and myoplasmic Ca2 + in cardiac Purkinje fibers.