beta-adrenergic agonists stimulate Na+-K+-Cl- cotransport by inducing intracellular Ca2+ liberation in crypt cells

Epinephrine and beta-adrenergic agonists (beta1 and beta2 for isoproterenol, beta1 for dobutamine, beta2 for salbutamol) stimulated K+ (or 86Rb) influx mediated by the Na+-K+-2Cl- cotransporter and the Na+-K+ pump in isolated colonic crypt cells. Preincubation with bumetanide abolished the epinephrine effect on the Na+-K+ pump, suggesting that the primary effect is on the cotransporter. Maximal effect was obtained with 1 microM epinephrine with an EC50 of 91.6 +/- 9.98 nM. Epinephrine-induced K+ transport was blocked by propranolol with an IC50 of 134 +/- 28.2 nM. alpha-Adrenergic drugs did not modify K+ transport mechanisms. Neither Ba2+ nor tetraethylammonium nor DIDS modified the adrenergic enhancement on the cotransporter. In addition, epinephrine did not affect K+ efflux. Dibutyryl cAMP did not alter K+ transport. Reduction of extracellular Ca2+ to 30 nM did not influence the response to epinephrine. However, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM abolished epinephrine-induced K+ transport. Ionomycin increased Na+-K+-2Cl- cotransport activity. Moreover, epinephrine increased intracellular Ca2+ concentration in a process inhibited by propranolol. In conclusion, epinephrine stimulated the Na+-K+-2Cl- cotransporter in a process mediated by beta1- and beta2-receptors and modulated by intracellular Ca2+ liberation.