Vol. 54, Issue 3, 559-568, September 1998

The Anesthetic Steroid (+)-3-Hydroxy-5-androstane-17-carbonitrile Blocks N-, Q-, and R-Type, but Not L- and P-Type, High Voltage-Activated Ca²⁺ Current in Hippocampal and Dorsal Root Ganglion Neurons of the Rat

Yasunori M. Nakashima,¹ Slobodan M. Todorovic, Douglas F. Covey, and Christopher J. Lingle

Departments of Anesthesiology (Y.M.N., S.M.T., C.J.L.) and Molecular Biology and Pharmacology (D.F.C.), Washington University School of Medicine, St. Louis, Missouri 63110

High voltage-activated (HVA) Ca²⁺ current (I_Ca) was recorded from neonatal rat hippocampal and adult rat dorsal root ganglion neurons. In both cell types, (+)-3-hydroxy-5-androstane-17-carbonitrile [(+)-ACN], a neuroactive steroid, had no effect on nifedipine- (L-type) or -agatoxin IVA- (P-type) sensitive I_Ca. Selective blockade of N-type current with -conotoxin GVIA and of Q-type current with -conotoxin MVIIC indicated that (+)-ACN inhibits both N- and Q-type current components in both cell types. Current persisting after blockade of all other current components (R-type) was also sensitive to (+)-ACN. Half-blockade of (+)-ACN-sensitive HVA current occurred in the range of 3-25 µM, with N-type current somewhat more sensitive than Q- or R-type. The (+)-ACN enantiomer, ()-ACN, and pregnanolone were somewhat less effective at inhibiting total HVA current than (+)-ACN, whereas several steroid analogs, including alfaxalone, were relatively ineffective at inhibiting total HVA current. Neither guanosine-5'-O-(2-thio)diphosphate nor guanosine-5'-O-(3-thio)triphosphate altered the ability of (+)-ACN to inhibit HVA current in dorsal root ganglion neurons, indicating that (+)-ACN acts directly on Ca²⁺ channels. The partial selectivity exhibited by (+)-ACN among different HVA current components suggests that manipulations of steroid analogues may be a useful strategy in the generation of more selective, more potent, small-molecular-weight HVA channel blockers.