DOPAMINERGIC PROPERTIES OF CULTURED RAT CAROTID-BODY CHEMORECEPTORS GROWN IN NORMOXIC AND HYPOXIC ENVIRONMENTS

Using dissociated carotid body (CB) cultures prepared from neonatal (p ostnatal;days 5-7; P7) or juvenile (postnatal day 19-20; P20) rats, we compared catecholaminergic properties and mechanisms of O-2 sensing i n glomus cells grown in normoxic (Nor; 20% O-2) and chronically hypoxi c (CHox; 6% O-2) environments for up to 2 weeks. In Nor cultures, basa l dopamine (DA) release, determined by HPLC and normalized to the numb er of tyrosine hydroxylase-positive glomus cells present, was similar for P7 and P20 cultures (similar to 0.3 pmol/1,000 cells/15 min) and w as unaffected by culture duration (2 vs. 12 days). Acute hypoxia (5 an d 10% O-2) caused a dose-dependent stimulation (6x and 3x basal, respe ctively) in DA release, that was inhibited by nifedipine (10 mu M). DA release was also stimulated by high extracellular K+ (30 mM) and iber iotoxin (200 nM), a selective blocker of Po-2-regulated, Ca-dependent K+ channel in glomus cells. The stimulatory effect of iberiotoxin was similar to 5% O-2 in P20 cultures, but substantially less (about one-h alf) in P7 cultures. In contrast, in CHox cultures, basal DA release w as substantially elevated, similar to 8x Nor levels, although this did not correlate with significant differences in stores. Further, wherea s acute hypoxia (5% O-2) and high KC also stimulated DA release in CHo x cultures (similar to 2x and similar to 3x basal), iberiotoxin (200 n M) did not. Thus, after chronic hypoxia in vitro, there is an enhanced basal catecholamine release and an apparent down-regulation of functi onal Ca-dependent K+ channels in CB chemoreceptors. These cellular ada ptations may relate to changes in CB chemosensitivity during chronic h yperemia.