Dopamine-dependent inhibition of jejunal Na+-K+-ATPase during high-salt diet in young but not in adult rats

During high-salt diet endogenous dopamine (DA) reduces jejunal sodium trans port in young but not in adult rats. This study was designed to evaluate wh ether this effect is mediated, at the cellular level, by inhibition of Na+- K+-ATPase activity. Enzyme activity was determined in isolated jejunal cell s by the rate of [gamma-P-32]ATP hydrolysis. Cells were obtained from weanl ing and adult rats fed either with high- or normal-salt diet. In 20-day-old but not in 40-day-old rats Na+-K+-ATPase activity was significantly reduce d during high-salt diet. This inhibition was abolished by a blocker of DA s ynthesis. The decreased activity was associated with a decreased alpha(1)-s ubunit at the plasma membrane. During high-salt diet there was an increase in DA content in jejunal cells from 20-day-old rats, associated with a para llel decrease in 5-hydroxytryptamine compared with normal-salt diet. In 40- day-old rats, however, the catecholamine level remained unchanged during hi gh-salt diet. Incubation of isolated jejunal cells with DA resulted in a do se-dependent inhibition of Na+-K+-ATPase activity in 20- but not in 40-day- old rats. We conclude that during high-salt diet, jejunal Na+-K+-ATPase in 20-day-old rats is inhibited, and this effect is likely to be mediated by l ocally formed DA.