VOLATILE ANESTHETICS INHIBIT VOLTAGE-DEPENDENT CA2-MUSCLE CELLS( CHANNELS IN PORCINE TRACHEAL SMOOTH)

The relaxation of airway smooth muscle by volatile anesthetics is asso ciated with a decreased concentration of intracellular free Ca2+. We h ypothesized that inhibition of the entry of extracellular Ca2+ contrib utes to the relaxation. We therefore examined the effects of halothane , isoflurane, and sevoflurane on macroscopic voltage-activated Ca2+ cu rrents (I-Ca) in porcine tracheal smooth muscle cells, using the whole cell patch-clamp technique. All three volatile anesthetics significan tly inhibited I-Ca in a dose-dependent manner with no apparent shift i n the voltage dependence of induced I-Ca. The order of inhibitory pote ncies for I-Ca was halothane > isoflurane > sevoflurane. When data wer e plotted as a function of the estimated anesthetic concentrations in the lipid phase, the potencies for inhibition of I-Ca by the three ane sthetics were indistinguishable. We conclude that volatile anesthetics have an inhibitory effect on I-Ca of porcine tracheal smooth muscle c ells at clinically relevant concentrations and that the inhibitory pot encies of volatile anesthetics on I-Ca are closely related to their li pid-phase solubilities.