Abstract
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 α1H 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 (α1B, α1C, α1D and α1E), with the exception of α1A. Western blot analysis and pharmacology with ω-agatoxin IVA (1 μM) confirmed that MPG neurons lack the α1A 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, ω-conotoxin GVIA-sensitive N-type (α1B) currents constituted 57 ± 5% (n = 9) and 60 ± 3% (n = 6), respectively; nimodipine-sensitive L-type (α1C and α1D) currents made up 17 ± 4% and 14 ± 2%, respectively; and nimodipine-resistant and ω-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 α1E/β2a/α2δ 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.
Footnotes
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This study was supported by Grant 03-PJ1-PG10-21300-0012 from the Korea Health 21 R&D project, Ministry of Health Welfare, Republic of Korea.
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doi:10.1124/jpet.105.098210.
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ABBREVIATIONS: VACC, voltage-activated Ca2+ channel(s); HVA, high voltage-activated; LVA, low voltage-activated; MPG, major pelvic ganglia; RT-PCR, reverse transcription-polymerase chain reaction; GFP, green fluorescence protein; HEK, human embryonic kidney; MS, methanesulfonate.
- Received November 7, 2005.
- Accepted February 6, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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