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.
del Castillo
J R
JR
Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, Caracas 1020-A, Venezuela. jdelcas@cbb.ivic.ve
Arévalo
J C
JC
Burguillos
L
L
Súlbaran-Carrasco
M C
MC
D018663:Adrenergic Agents / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D004837:Epinephrine / Q000494:pharmacology; D006168:Guinea Pigs; D007425:Intracellular Membranes / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000378:metabolism; D015290:Second Messenger Systems / Q000502:physiology; D028021:Sodium-Potassium-Chloride Symporters
D018663:Adrenergic Agents; D000318:Adrenergic beta-Agonists; D002352:Carrier Proteins; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D011188:Potassium; D002118:Calcium; D004837:Epinephrine