PHENOTYPE-SPECIFIC EXPRESSION OF T-TYPE CALCIUM CHANNELS IN NEURONS OF THE MAJOR PELVIC GANGLION OF THE ADULT MALE-RAT

1. Neurons from the major pelvic ganglia (MPG) of adult male rats were enzymatically dissociated and the neurochemical phenotype and Ca2+ cu rrent properties examined. 2. Neurons were divided into two subpopulat ions based on the presence or absence of low threshold T-type Ca2+ cha nnels. The subpopulation of neurons expressing T-type Ca2+ channels wa s characterized by a mean diameter of 34 mu m, a mean membrane capacit ance (C-m) of 72 pF, tyrosine hydroxylase immunoreactivity (TH-IR), a lack of NADPH diaphorase (NADPHd) reactivity and a high degree of alph a(2)-adrenoceptor-mediated Ca2+ current inhibition (60%). 3. The subpo pulation of neurons without overt T-type Ca2+ channels lad a mean diam eter of 23 mu m, a mean C-m of 30 pF, a lack of TH-IR and a moderate d egree 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 dete rmined from omega-conotoxin GVIA inhibition, and L-type Ca2+ channels (<10%), as determined from nifedipine inhibition, to the whole-cell Ca 2+ current was similar for both subpopulations of neurons. 5. These da ta indicate that the MPG contain at least two subpopulations of postga nglionic neurons, i.e. adrenergic and non-adrenergic, with distinct el ectrophysiological and neurochemical properties. Furthermore, we propo se that the presence or absence of T-type Ca2+ channels provides an el ectrophysiological means of identifying adrenergic and non-adrenergic phenotype, respectively, in neurons of the male rat MPG.