The Anesthetic Steroid (+)-3α-Hydroxy-5α-androstane-17β-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
- Departments of 1Anesthesiology (Y.M.N., S.M.T., C.J.L.) and2Molecular Biology and Pharmacology (D.F.C.), Washington University School of Medicine, St. Louis, Missouri 63110
Abstract
High voltage-activated (HVA) Ca2+ current (ICa) was recorded from neonatal rat hippocampal and adult rat dorsal root ganglion neurons. In both cell types, (+)-3α-hydroxy-5α-androstane-17β-carbonitrile [(+)-ACN], a neuroactive steroid, had no effect on nifedipine- (L-type) or ω-agatoxin IVA- (P-type) sensitive ICa. Selective blockade of N-type current with ω-conotoxin GVIA and of Q-type current with ω-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.
Footnotes
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Send reprint requests to: Dr. Chris Lingle, Washington University School of Medicine, Dept. of Anesthesiology, Box 8054, St. Louis, MO 63110. E-mail:clingle{at}morpheus.wustl.edu
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↵1 Current affiliation: Surgical Operating Theater, Kyushu University Hospital, Fukuoka, 812-8582, Japan.
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This work was supported by National Institutes of Health Grant GM47969 (D.F.C. and C.J.L.).
- Abbreviations:
- HVA
- high voltage activated
- (+)-ACN
- (+)-3α-hydroxy-5α-androstane-17β-carbonitrile
- IBa
- Ba2+ current
- ICa
- Ca2+ current
- ICl
- Cl− current
- DMSO
- dimethylsulfoxide
- I-V
- current-voltage
- PS
- pregnenolone sulfate
- CgTx
- conotoxin
- Aga
- agatoxin
- DRG
- dorsal root ganglion
- GDPβS
- guanosine-5′-O-(2-thio)diphosphate
- GTPγS
- guanosine-5′-O-(3-thio)triphosphate
- EGTA
- ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
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- Received January 29, 1998.
- Accepted May 18, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
