Pyrimidinoceptors-mediated activation of Ca2+-dependent Cl- conductance inmouse endometrial epithelial cells

Previous studies have demonstrated the activation of endometrial Cl- secret ion through P-2Y2 (P-2U) purinoceptors by extracellular ATP. The present st udy further explored the presence of pyrimidine-sensitive receptors in the primary cultured mouse endometrial epithelial cells using the short-circuit current (I-SC) and whole-cell patch-clamp techniques. UDP induced a transi ent increase in I-SC in a concentration-dependent manner (EC50 approximate to 8.84 mu M). The UDP-induced I-SC was abolished after pretreating the epi thelia with a calcium chelator, 1,2-bis-(2-aminophenoxy)-ethane-N,N,N'N' te traacetic acid-acetomethyl eater (BAPTA-AM), suggesting the dependence of t he I-SC on cytosolic free Ca2+. The type of receptor involved was studied b y cross-desensitization between ATP and UDP. ATP or UDP desensitized its su bsequent I-SC response. However, when ATP was added after UDP, or vice vers a, a second I-SC response was observed, indicating the activation of distin ct receptors, possibly pyrimidine-sensitive receptors in addition to P-2Y2 (P-2U) receptors. Similar results were observed in the patch-clamp experime nts where UDP and ATP were shown to sequentially activate whole-cell curren t in the same cell. The UDP-activated whole-cell current exhibited outward rectification with delay activation and inactivation at depolarizing and hy perpolarizing voltages, respectively. In addition, the UDP-evoked whole-cel l current reversed near the equilibrium potential of Cl- in the presence of a Cl- gradient across the membrane, and was sensitive to 4,4'-diisothiocya nostilbene-2,2'-disulfonic acid (DIDS), indicating the activation of Ca2+-a ctivated Cl- conductance. These characteristics were very similar to that o f the ATP-activated whole-cell current. Taken together, our findings indica te the presence of distinct receptors, pyrimidinoceptors and P-2Y2 (P-2U) r eceptors in mouse endometrial epithelial cells. These distinct receptors ap pear to converge on the same Ca2+-dependent Cl- channels. (C) 2000 Elsevier Science B.V. All rights reserved.