Purpose: This study was undertaken to assess the effect of ketamine on L-type calcium channel current (I(Ca)) and membrane action potential in the bullfrog single atrial myocyte.
Methods: Bullfrog single atrial myocytes were prepared by enzymatic dispersion. Whole-cell voltage-clamp technique and current clamp technique were used to monitor I(Ca), membrane resting potential, and action potential.
Results: Ketamine (10(-5)-10(-3) M) showed dose-dependent inhibition of I(Ca) in a reversible manner. The 50% inhibitory concentration (IC(50)) of ketamine on I(Ca) was estimated to be 0.92 x 10(-5) M. Use-dependent block of I(Ca) was not observed. The resting membrane potential was depolarized at a high concentration (10(-4) M) of ketamine. Reduction of the plateau phase and prolonged duration of the action potential were observed in the presence of a high concentration of ketamine (10(-4) M).
Conclusion: Ketamine has an inhibitory effect on I(Ca) in the bullfrog single atrial myocyte, and a high dose (10(-4) M) of ketamine prolonges the duration of the action potential. The mechanism of inhibition of I(Ca) seems to be a direct effect on the L-type calcium channel, not like an open channel blocker.