Different regulatory pathways involved in ATP‐stimulated chloride secretion in rat epididymal epithelium

Abstract

The regulatory pathways involved in the ATP-stimulated Cl- secretion across rat epididymal epithelium were investigated by the short-circuit current (ISC) technique. Biphasic characteristic was observed in the ISC responded to ATP (0.01-10 microM). Inhibitor of P1 receptor, 8-phenyltheophylline (up to 100 microM), did not have any effect on both phases of the ATP-stimulated ISC. The order of potency for stimulation of the two phases in ISC was ATP > ADP >> AMP, adenosine, consistent with the presence of P2-purinoceptors. Cl- channel blocker, disulfonic acid stilbene (DIDS, 300 microM), only inhibited the first peak of the ATP-stimulated ISC while diphenylamine-dicarboxylic acid (DPC, 1 mM) reduced both, indicating the involvement of different conductance pathways. DIDS was found to have an inhibitory effect on Ca(2+)-activated ISC (induced by ionomycin, 10 microM) but not cAMP-activated ISC (induced by forskolin, 1 microM) which could only be blocked by DPC. Both peaks of the ATP-activated ISC could be significantly inhibited by pretreatment with a Ca(2+)-chelating agent, BAPTA-AM (50 microM). An increase in cellular cAMP content upon stimulation of ATP was measured by radioimmunoassay. No significant increase in cAMP production was observed in cells stimulated with adenosine. The ATP-induced cAMP increase was prevented by pretreatment with BAPTA-AM (100 microM) indicating that cAMP production upon ATP stimulation was secondary to an increase in intracellular Ca2+ concentration. These results indicate that the ATP-stimulated Cl- secretion could be mediated by Ca2+ and cAMP-dependent regulatory pathways giving rise to the biphasic nature of the ATP-induced ISC.

Infection by Toxoplasma gondii , a severe parasite in neonates and AIDS patients, causes impaired anion secretion in airway epithelia

“…Extracellular ATP is considered a key signaling molecule to maintain the normal homeostasis of these processes in airway epithelia (40,41). Our studies in mouse trachea epithelia show that the response of the ATP-stimulated Cl − secretion consisted of an initial spike and a long-term component, which is consistent with previous studies in various organs (23)(24)(25). P2Y2-R is a Gq-coupled protein that is activated by extracellular ATP to promote Gq-dependent activation of PLC, which in turn regulates calcium flux and protein kinase C (PKC) activity, by an IP3 and diacylglycerol (DAG)-dependent mechanism, in Schwann cells and eye suprachoroid (42,43).…”

“…Previous studies on extracellular ATP-induced transepithelial Cl − transport in different epithelial cells have shown that the time course for the ATP response is biphasic. Different regulatory pathways are involved in mediating the ATP-induced short-circuit current (I sc ), such as the cAMP-dependent and the traditional P2-purinoceptor-linked Ca 2+ -dependent or P1-like receptordependent pathways, which activate different Cl − channels (23)(24)(25). In this study, we investigate the I sc response to extracellular ATP at 10 μM in mice trachea epithelia.…”

Differential Regulations between Adenosine Triphosphate (ATP)– and Uridine Triphosphate–Induced Cl−Secretion in Bovine Tracheal Epithelium

“…Although there have been a number of studies on transepithelial Cl Ϫ transport by extracellular ATP andրor other nucleotides (5,9,(14)(15)(16), few reports made reference to such an Isc having two distinct peaks (26,27). We also found that the responses of Isc were different between ATP and UTP.…”

Bicarbonate-rich choleresis induced by secretin in normal rat is taurocholate-dependent and involves AE2 anion exchanger

“…This possibility is not ruled out by the observed inhibition of acetylcholine-stimulated increase in biliary HCO 3 Ϫ excretion by intravascular DIDS. 25 In a context of possible acetylcholine-induced vascular disturbances in the liver, impermeant DIDS may manage to reach bile duct lumen and interact extracellularly with different carriers such as Ca 2ϩ -activated Cl Ϫ channels, 46 anion exchangers, and other HCO 3 Ϫ transporters. Alternatively, DIDS may inhibit basolateral factors presumably involved in acetylcholine signaling (which differs from secretin signaling).…”