EFFECT OF KB-2796, A NEW DIPHENYLPIPERAZINE CA2(+) ANTAGONIST, ON VOLTAGE-DEPENDENT CA2(+) CURRENTS AND OXIDATIVE-METABOLISM IN DISSOCIATED MAMMALIAN CNS NEURONS

The effects of KB-2796, 1-[bis(4-fluorophenyl)methyl]-4-(2,3,4-trimethoxybenzyl)piperazine-2HCl, on the low- and high-voltage activated Ca2+ currents (LVA and HVA I(Ca) respectively) and on oxidative metabolism were studied in neurons freshly dissociated from rat brain. KB-2796 reduced the peak amplitude of LVA I(Ca) in a concentration-dependent manner with a threshold concentration of 10(-7) M when the LVA I(Ca) was elicited every 30 s in the external solution with 10 mM Ca2+. The concentration for half-maximum inhibition (IC50) was 1.9 X 10(-6) M. At 10(-5) M or more of KB-2796, a complete suppression of the LVA I(Ca) was observed in the majority of neurons tested. There was no apparent effect on the current-voltage (I-V) relationship and the current kinetics. KB-2796 delayed the reactivation and enhanced the inactivation of the Ca2+ channel for LVA I(Ca) voltage- and time-dependently, suggesting that KB-2796 preferentially binds to the inactivated Ca2+ channel. KB-2796 at a Concentration of 3.0 x 10(-6) M also decreased the peak amplitude of the HVA I(Ca) without shifting the I-V relationship. In addition, KB-2796 reduced the oxidative metabolism (the formation of reactive oxygen species) of the neuron in a concentration-dependent manner with a threshold concentration of 3 x 10(-6) M. It is suggested that the inhibitory action of KB-2796 on the neuronal Ca2+ influx and the oxidative metabolism, in combination with a cerebral vasodilatory action, may reduce ischemic brain damage.