Sarco-endoplasmic ATPase blocker 2,5-di(tert-butyl)-1,4-benzohydroquinone inhibits N-, P-, and Q- but not T-, L-, or R-Type calcium currents in central and peripheral neurons

The effects of 2,5-di(tert-butyl)-1,4-benzohydroquinone (tBHQ), a synthetic phenolic antioxidant and a blocker of the sarcoendoplasmic ATPase, were ev aluated on low and high voltage-activated Ca2+ currents (ICas) with rodent dorsal root ganglion, hippocampal, and motor neurons. In all cell types tes ted, tBHQ (IC50 = 35 mu M) blocked ICa at concentrations used to inhibit sa rco-endoplasmic ATPase. This effect was specific to tBHQ because the other sarco-endoplasmic reticulum calcium ATPase pump inhibitors (thapsigargin an d cyclopiazonic acid) had no effect. Selective blockade of the N-type curre nt with omega-conotoxin GVIA and of P-(motoneuron) or Q-type currents (hipp ocampal neuron) with omega-agatoxin IVA indicated that tBHQ inhibited N, P, and Q types of ICa. tBHQ had no effect on nitrendipine-sensitive (L-type) and residual drug-resistant (R-type) ICa, nor on the low voltage-activated T-type ICa. Contrary to neuronal cells, the L-type ICa was inhibited by tBH Q in a differentiated mouse neuroblastoma and rat glioma hybrid cell line. Injection of cDNAs encoding the alpha 1A, alpha 1B, alpha 1C, and alpha 1E subunits into oocytes showed that tBHQ blocked ICas at the level of the por e-forming protein. This effect of tBHQ on ICa should be considered when int erpreting results obtained with tBHQ used on neuronal preparations. It also may be useful for developing new strategies for the generation of more pot ent intracellular calcium transient inhibitors.