AJP - Lung Cellular and Molecular Physiology, Vol 268, Issue 2 187-L191, Copyright © 1995 by American Physiological Society
Volatile anesthetics inhibit voltage-dependent Ca2+ channels in porcine tracheal smooth muscle cells
M. Yamakage, C. A. Hirshman and T. L. Croxton
Department of Anesthesiology, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
The relaxation of airway smooth muscle by volatile anesthetics is
associated with a decreased concentration of intracellular free Ca2+. We
hypothesized that inhibition of the entry of extracellular Ca2+ contributes
to the relaxation. We therefore examined the effects of halothane,
isoflurane, and sevoflurane on macroscopic voltage-activated Ca2+ currents
(ICa) in porcine tracheal smooth muscle cells, using the whole cell
patch-clamp technique. All three volatile anesthetics significantly
inhibited ICa in a dose-dependent manner with no apparent shift in the
voltage dependence of induced ICa. The order of inhibitory potencies for
ICa was halothane > isoflurane > sevoflurane. When data were plotted
as a function of the estimated anesthetic concentrations in the lipid
phase, the potencies for inhibition of ICa by the three anesthetics were
indistinguishable. We conclude that volatile anesthetics have an inhibitory
effect on ICa of porcine tracheal smooth muscle cells at clinically
relevant concentrations and that the inhibitory potencies of volatile
anesthetics on ICa are closely related to their lipid-phase solubilities.
