Ketamine suppresses norepinephrine-induced inositol 1,4,5-trisphosphate formation via pathways involving protein kinase C.

UNLABELLED Inositol 1,4,5-trisphosphate (IP(3)) is not only involved in the physiologic regulation of excitation-contraction coupling, but could also play a role in cardiac pathophysiology. We investigated the mechanism of ketamine modulation of norepinephrine (NE)-induced IP(3) formation in neonatal rat cardiomyocytes. Ketamine 1 and 10 microM significantly decreased the IP(3) response to 1 microM NE by 27% and 43%, respectively. One micromolar TMB-8 (an intracellular calcium antagonist) produced 42% more decreases in IP(3) production than produced by ketamine alone. One hundred micromolar anthranilic acid (a phospholipase A(2) inhibitor) significantly decreased NE (1 microM)-induced IP(3) formation, and the inhibition was further enhanced by ketamine. Ten micromolar U 73122 (a phospholipase C inhibitor) did not significantly affect NE-induced IP(3) in the presence or absence of ketamine. One micromolar ketamine significantly inhibited staurosporine (a nonselective protein kinase C antagonist)-, bisindolylmaleimide (a selective protein kinase C antagonist)-, and wortmannin (a phosphatidylinositide 3-kinase antagonist)-stimulated IP(3) formation. In conclusion, ketamine suppresses NE-induced IP(3) production, and the inhibition is caused through pathways including protein kinase C and a decrease in intracellular Ca(2+) concentrations. IMPLICATIONS Ketamine inhibits norepinephrine-induced inositol 1,4,5-triphosphate formation in a dose-dependent manner via pathways that involve protein kinase C and a decrease in intracellular Ca(2+) concentrations.