Ontogenic aspects of D-1 receptor coupling to G proteins and regulation ofrat jejunal Na+, K+ ATPase activity and electrolyte transport

1 The present study examined the effect of dopamine on rat jejunal electrol yte transport (rheogenic transport and Na+, K+-ATPase activity) in adult (6 0-day old) and young (20-day old) animals. 2 In young rats, dopamine, in the presence of phentolamine, produced an inc rease in jejunal I-sc, this being completely abolished by SKF 83566, and no t changed by S-sulpiride. SKF 38393, but not quinerolane, also increased I- sc; this effect was abolished by SKF 83566 and ouabain, but not by furosemi de. In adult rats, dopamine in the presence of phentolamine (0.2 mu M) decr eased I-sc. 3 Na+, K+-ATPase activity in isolated jejunal epithelial cells from adult r ats was 2.4 fold that in young rats. In the presence of phentolamine, both dopamine and SKF 38393, but not quinerolane, significantly decreased jejuna l Na+, K+-ATPase activity in young animals but not in adult animals. 4 Binding [H-3]-Sch 23390 to membranes of jejunal mucosa revealed the prese nce of a single class of receptors in both young and adult rats, with simil ar K-D and B-max values. 5 GTP gamma S and cholera toxin inhibited jejunal Na+, K+-ATPase activity i n young, but not in adult rats. Co-incubation of pertussis toxin with dopam ine was found to potentiate the inhibitory effects of dopamine upon the enz yme in both young and adult rats. 6 Regulation of Na+, K+-ATPase activity by cholera toxin-sensitive G protei ns is absent in adult animals, and such difference may explain the failure of dopamine to inhibit intestinal Na+, K+-ATPase activity in adult rats.