BETA-ADRENERGIC STIMULATION OF CELLULAR K+ UPTAKE IN RAT DISTAL COLON

We recently demonstrated that the ratio between colonic K+ absorptive and K+ secretive pathways was higher in infant than in adult rats. To test the hypothesis that hormones selectively affect these pathways du ring ontogeny we examined the effect of adrenergic agonists on cellula r K+ uptake in distal colon from infant (10-day-old) and adult (50-day -old) rats. Here we describe that adrenaline (10(-5) M) increased tota l and ouabain-insensitive Rb-86 uptake in both age groups, but it did not affect ouabain-sensitive Rb-86 uptake. This stimulation was more p ronounced in adult than in infant rats. The effect of adrenaline was m ediated via beta-adrenergic receptors. Incubation in vitro with beta-a gonist. isoproterenol, stimulated SCH-28080-sensitive, i.e. H+.K+-AtPa se-dependent. Rb-86 uptake in adult but not in infant rats. The thresh old dose of beta-agonist was at 10(-7) M,nd the maximal activation was observed at 10(-5) M. In vivo inhibition of beta-adrenergic system wi th propranolol caused a significant decrease in H+.K+-ATPase-dependent Rb-86 uptake in infant but not in adult colon. In conclusion, this st udy suggests that the higher colonic K+ absorption in infant rats may be as a result of a selective beta-adrenergic up-regulation leading to stimulation of the apical H+,K+-ATPase.