Ketamine inhibits inositol 1,4,5-trisphosphate production depending on the extracellular Ca2+ concentration in neonatal rat cardiomyocytes.

UNLABELLED: We investigated the effect of ketamine on inositol 1,4,5-trisphosphate (IP3) formation in rat cardiomyocytes. After the addition of 1 micromol/L ketamine, IP3 production in the presence of 0.5, 1, 5, 10, and 30 mmol/L Ca2+ significantly decreased from 537.1+/-8.3, 590.7+/-12.9, 690.6+/-7.9, 754.8+/-12.5, and 823.7+/-15.2 pmol/mg protein to 467.0+/-8.3, 483.8+/-11.0, 512.6+/-21.3, 612.1+/-16.9, and 652.6+/-17.3 pmol/mg protein, respectively. When exposed to TMB-8 (a intracellular calcium inhibitor), IP3 production decreased significantly from 347.2+/-27.3 to 283.8+/-20.4 pmol/mg protein in the presence of 1 micromol/L ketamine, but A23187, which increases intracellular calcium, did not affect the inhibition of IP3 production by ketamine. These results demonstrate that ketamine decreases IP3 formation through inhibition of the calcium ion-sensing receptor and that IP3 formation reduced by ketamine is not affected by the alteration of intracellular calcium. IMPLICATIONS: Ketamine has a negative inotropic effect in isolated cardiomyocytes. The negative inotropic effect was associated with a decrease in inositol 1,4,5-trisphosphate production, and the inhibitory action was enhanced depending on the concentration of extracellular Ca2+.