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CELLULAR AND MOLECULAR

Expression Profiles of High Voltage-Activated Calcium Channels in Sympathetic and Parasympathetic Pelvic Ganglion Neurons Innervating the Urogenital System

Departments of Physiology (Y.-J.W., I.D.K., K.-S.P., J.-W.L., S.-W.J.) and Neurosurgery (K.W.), Institute of Basic Medical Science, Yonsei University Wonju College of Medicine, Wonju, Kangwon-Do, Republic of Korea

Among the autonomic ganglia, major pelvic ganglia (MPG) innervating the urogenital system are unique because both sympathetic and parasympathetic neurons are colocalized within one ganglion capsule. Sympathetic MPG neurons are discriminated from parasympathetic ones by expression of low voltage-activated Ca²⁺ channels that primarily arise from T-type _1H isoform and contribute to the generation of low-threshold spikes. Until now, however, expression profiles of high voltage-activated (HVA) Ca²⁺ channels in these two populations of MPG neurons remain unknown. Thus, in the present study, we dissected out HVA Ca²⁺ channels using pharmacological and molecular biological tools. Reverse transcription-polymerase chain reaction analysis showed that MPG neurons contained transcripts encoding all of the known HVA Ca²⁺ channel isoforms (_1B, _1C, _1D and _1E), with the exception of _1A. Western blot analysis and pharmacology with -agatoxin IVA (1 µM) confirmed that MPG neurons lack the _1A Ca²⁺ channels. Unexpectedly, the expression profile of HVA Ca²⁺ channel isoforms was identical in the sympathetic and parasympathetic neurons of the MPG. Of the total Ca²⁺ currents, -conotoxin GVIA-sensitive N-type (_1B) currents constituted 57 ± 5% (n = 9) and 60 ± 3% (n = 6), respectively; nimodipine-sensitive L-type (_1C and _1D) currents made up 17 ± 4% and 14 ± 2%, respectively; and nimodipine-resistant and -conotoxin GVIA-resistant R-type currents were 25 ± 3% and 22 ± 2%, respectively. The R-type Ca²⁺ currents were sensitive to NiCl₂ (IC₅₀ = 22 ± 0.1 µM) but not to SNX-482, which was able to potently (IC₅₀ = 76 ± 0.4 nM) block the recombinant _1E/_2a/₂ Ca²⁺ currents expressed in human embryonic kidney 293 cells. Taken together, our data suggest that sympathetic and parasympathetic MPG neurons share a similar but unique profile of HVA Ca²⁺ channel isoforms.

Address correspondence to: Dr. Seong-Woo Joeng, Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Kangwon-Do 220-701, Republic of Korea. E-mail: swjeong{at}wonju.yonsei.ac.kr