Ca2+ channel antagonist U-92032 inhibits both T-type Ca2+ channels and Na+ channels in hippocampal CA1 pyramidal neurons

The effects of 7-[[4-[bis(4-fluorophenyl)-methyl]-1-piperazinyl]methyl]-2-[(2-hydroxyethyl)amino] 4-(1-methylethyl)-2,4,6-cycloheptatrien-1-one (U-92032), a newly described Ca2+ channel blocker, on voltage-gated ionic currents were measured. Whole cell voltage-clamp records were obtained from acutely isolated CA1 hippocampal pyramidal neurons from 7- to 14-day-old rats. Dimethyl sulfoxide, at either 0.01% or 0.1%, partially inhibited T-type Ca2+ currents (similar to 20% inhibition) but not high-voltage-activated (HVA) Ca2+ currents. Ethanol (0.2%) did not Effect Ca2+ currents. U-92032 selectively inhibited T-type Ca2+ currents (median inhibiting concentration similar to 500 nM). HVA Ca2+ currents were less sensitive, with similar to 75% of the current resistant at 10 mu M. Inhibition of Ca2+ currents was reversible. U-92032 inhibited Na+ currents at concentrations similar to those required for T-type currents (>33% block at 1 mu M). Block of Na+ currents took several minutes to develop and was irreversible. Voltage-gated K+ currents were insensitive to U-92032 (1 or 10 mu M). These results indicate that U-92032 inhibits both T-type Ca2+ channels and Na+ channels, constraining its utility in certain studies. Among Ca2+ channels, however, U-92032 should prove a useful tool for distinguishing physiological contributions of T-type channels.