Abstract
The effects of thiopental on Ca<sup>2+</sup> currents and intracellular Ca<sup>2+</sup> transient in single atrial cells from guinea pigs were studied by means of a whole-cell voltage-clamp method and Ca<sup>2+</sup>-sensitive fluorescent dye. Thiopental inhibited L-type voltage-dependent Ca<sup>2+</sup> currents in a concentration-dependent manner (IC<sub>50</sub> = 2.8·10<sup>–5</sup> mol/l). Moreover, the mode of Ca<sup>2+</sup> current inhibition by thiopental showed no use dependency. Electrical stimulation-induced intracellular Ca<sup>2+</sup> transient was significantly suppressed by 10<sup>–5</sup> mol/l thiopental. However, the caffeine-sensitive Ca<sup>2+</sup> releasing pathway from sarcoplasmic reticulum was not affected by thiopental. Our results indicate that thiopental inhibits L-type Ca<sup>2+</sup> currents, but not release of Ca<sup>2+</sup> from sarcoplasmic reticulum. These results suggest that the negative inotropic action of thiopental is mainly due to inhibition of L-type Ca<sup>2+</sup> channels in guinea pig atrial myocytes.
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