[The dual effect of ketamine on dopamine release from rat pheochromocytoma (PC-12) cells].

Ketamine is known to increase arterial pressure and heart rate with its sympathomimetic action. However, it also relaxes vascular smooth muscle and causes hypotension. We studied such a bipartite effect in terms of ketamine induced changes of dopamine (DA) release from rat pheochromocytoma (PC-12) cells as a model of sympathetic nervous system. Without KCl stimulation, ketamine increased the DA release from PC-12 cells in a dose-related fashion (10(-4)M: 2.6 +/- 0.4, 10(-3)M : 7.5 +/- 0.3, 10(-2)M: 27.1 +/- 3.2%). The similar increase of DA release was observed with absence of extracellular Ca2+. Exposure of KCl (50 mM) to PC-12 cells increased the DA efflux from 1.7 +/- 0.4 to 14.2 +/- 0.8% (P < 0.001). The release of DA stimulated by KCl (50 mM) was reduced to 9.0 +/- 1.0% and 11.4 +/- 0.3% in the presence of ketamine 5 x 10(-4)M and 10(-3)M respectively, and increased with the ketamine concentration of 10(-3)M. These findings indicate that ketamine depresses DA efflux related to membrane depolarization (K+) but it promotes a number of spontaneous DA efflux.