Neurotransmitters inhibit the omega-conotoxin-sensitive component of Ca current in neuroblastoma x glioma hybrid (NG 108-15) cells, not the nifedipine-sensitive component

Abstract

Voltage-dependent calcium currents (ICa) in NG 108-15 cells consisted of three pharmacologically distinct components: a transient low-voltage-activated (LVA) current, sensitive to Ni2+; a high-voltage-activated (HVA) current sensitive to the dihydropyridine antagonist, nifedipine and a HVA current sensitive to omega-conotoxin GVIA (CgTx). The voltage sensitivities and decay kinetics of the two HVA currents were indistinguishable. The neurotransmitters acetylcholine (ACh) and noradrenaline inhibited ICa. This inhibition was not occluded by Ni2+ or nifedipine, but was abolished by CgTx. It is therefore concluded that the neurotransmitter-sensitive component of ICa is restricted to that component of HVA current inhibitable by omega-conotoxin.