REGULATION OF CL- SECRETION BY EXTRACELLULAR ATP IN CULTURED MOUSE ENDOMETRIAL EPITHELIUM

The present study explored regulation of electrogenic ion transport ac ross cultured mouse endometrial epithelium by extracellular ATP using the short-circuit current (I-SC) and the patch-clamp techniques. The c ultured endometrial monolayers responded to apical application of ATP with an increase in I-SC in a concentration-dependent manner (EC(50) a t 3 mu M). Replacement of Cl- in the bathing solution or treatment of the cells with Cl- channel blockers, DIDS and DPC, markedly reduced th e I-SC, indicating that a substantial portion of the ATP-activated I-S C was Cl--dependent. Amiloride at a concentration (10 mu M) known to b lock Na+ channels was found to have no effect on the ATP-activated I-S C excluding the involvement of Na+ absorption. Adenosine was found to have little effect on the I-SC excluding the involvement of P-1 recept ors. The effect of UTP, a potent P-2U receptor agonist on the I-SC was similar to that of ATP while potent P-2X agonist, alpha-beta-Methylen e adenosine 5'-triphosphate (alpha-beta-M-ATP) and P-2Y agonist, 2-met hylthio-adenosine triphosphate (2-M-ATP), were found to be ineffective . The effect of ATP on I-SC was mimicked by the Ca2+ ionophore, ionomy cin, indicating a role of intracellular Ca2+ in mediating the ATP resp onse. Confocal microscopic study also demonstrated a rise in intracell ular Ca2+ upon stimulation by extracellular ATP. In voltage-clamped en dometrial epithelial cells, ATP elicited a whole-cell Cl- current whic h exhibited outward rectification and delayed activation and inactivat ion at depolarizing and hyperpolarizing voltages, respectively. The re sults of the present study demonstrate the presence of a regulatory me chanism involving extracellular ATP and P-2U purinoceptors for endomet rial Cl- secretion.