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+ 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.