Phenotype-specific expression of T-type calcium channels in neurons of the major pelvic ganglion of the adult male rat.

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1. Neurons from the major pelvic ganglia (MPG) of adult male rats were enzymatically dissociated and the neurochemical phenotype and Ca2+ current properties examined. 2. Neurons were divided into two subpopulations based on the presence or absence of low threshold T-type Ca2+ channels. The subpopulation of neurons expressing T-type Ca2+ channels was characterized by a mean diameter of 34 microns, a mean membrane capacitance (Cm) of 72 pF, tyrosine hydroxylase immunoreactivity (TH-IR), a lack of NADPH diaphorase (NADPHd) reactivity and a high degree of alpha 2-adrenoceptor-mediated Ca2+ current inhibition (60%). 3. The subpopulation of neurons without overt T-type Ca2+ channels had a mean diameter of 23 microns, a mean Cm of 30 pF, a lack of TH-IR and a moderate degree of alpha 2-adrenoceptor-mediated Ca2+ current inhibition (27%). About 50% of this subpopulation stained positively for NADPHd. 4. The contribution of high threshold N-type Ca2+ channels (60-70%), as determined from omega-conotoxin GVIA inhibition, and L-type Ca2+ channels (< 10%), as determined from nifedipine inhibition, to the whole-cell Ca2+ current was similar for both subpopulations of neurons. 5. These data indicate that the MPG contain at least two subpopulations of postganglionic neurons, i.e. adrenergic and non-adrenergic, with distinct electrophysiological and neurochemical properties. Furthermore, we propose that the presence or absence of T-type Ca2+ channels provides an electrophysiological means of identifying adrenergic and non-adrenergic phenotype, respectively, in neurons of the male rat MPG.

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