Key result
Thiopental inhibited L-type voltage-dependent Ca2+ currents in a concentration-dependent manner (IC50=2.8x10^-5 mol/l) and suppressed electrical stimulation-induced intracellular Ca2+ transient.
Thiopental's negative inotropic action is mainly due to the inhibition of L-type Ca2+ channels rather than affecting sarcoplasmic reticulum Ca2+ release.
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Thiopental may depress contractility via L-type Ca2+ inhibition in animal models; leaves open translation to human myocardium or clinical anesthesia.
The effects of thiopental on Ca2+ currents and intracellular Ca2+ transient in single atrial cells from guinea pigs were studied by means of a whole-cell voltage-clamp method and Ca2+-sensitive fluorescent dye. Thiopental inhibited L-type voltage-dependent Ca2+ currents in a concentration-dependent manner (IC50=2.8.10(-5) mol/l). Moreover, the mode of Ca2+ current inhibition by thiopental showed no use dependency. Electrical stimulation-induced intracellular Ca2+ transient was significantly suppressed by 10(-5) mol/l thiopental. However, the caffeine-sensitive Ca2+ releasing pathway from sarcoplasmic reticulum was not affected by thiopental. Our results indicate that thiopental inhibits L-type Ca2+ currents, but not release of Ca2+ from sarcoplasmic reticulum. These results suggest that the negative inotropic action of thiopental is mainly due to inhibition of L-type Ca2+ channels in guinea pig atrial myocytes.
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Kimura et al. (2007) studied this question. Thiopental was evaluated on L-type voltage-dependent Ca2+ currents and intracellular Ca2+ transient (IC50=2.8.10(-5) mol/l). Thiopental inhibited L-type voltage-dependent Ca2+ currents in a concentration-dependent manner (IC50=2.8x10^-5 mol/l) and suppressed electrical stimulation-induced intracellular Ca2+ transient.
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