Abstract

The effects of halothane (0.75% and 1.5%) and isoflurane (2.6%) on macroscopic Ca2+ and K+ channel currents (ICa and IK, respectively) were investigated in voltage-clamped vascular muscle cells from the canine coronary artery. Single coronary arterial cells were dialyzed with K+ glutamate solution and superfused with Tyrode's solution for measurement of IK (n = 45). Stepwise depolarization from a holding potential of -60 mV to beyond -30 mV elicited an outward, slowly inactivating IK that had a macroscopic slope conductance of 18 nS. IK was reduced 75% by 10 mM 4-aminopyridine, a K+ channel antagonist. Compared to 4-aminopyridine, halothane at 0.75% and 1.5% reduced peak IK amplitude only by 14 +/- 2% and 36 +/- 3%, respectively. At approximately equianesthetic concentrations, 2.6% isoflurane suppressed IK less than did 1.5% halothane, reducing peak amplitude by 15 +/- 3%. In other sets of experiments, cells were dialyzed with 120 Cs(+)-glutamate solution and superfused with 10 mM BaCl2 or CaCl2 solutions to isolate ICa (n = 39) pharmacologically. Under these conditions, progressive depolarizing steps from -60 mV elicited a small inward current, which was potentiated 3.4-fold by equimolar substitution of Ba2+ for Ca2+ in the external solution and was blocked by 1 microM nifedipine. This inward current, which resembled L-type ICa, was blocked 37 +/- 4% and 70 +/- 4% in the presence of 0.75% and 1.5% halothane, respectively. Isoflurane (2.6%) also decreased ICa by 55 +/- 5%. It appears that while halothane and isoflurane suppress both IK and ICa, these anesthetics preferentially reduce ICa.(ABSTRACT TRUNCATED AT 250 WORDS)