Cl- currents activated via purinergic receptors in Xenopus follicles

Ionic currents elicited via purinergic receptors located in themembrane of Xenopus follicles werestudied using electrophysiological techniques. Follicles responded toATP-activating inward currents with a fast time course(F_in). InRinger solution, reversal potential (E_rev) ofF_in was 22mV, which did not change with external substitutions ofNa⁺ orK⁺, whereas solutions containing50 or 5% of normal Clconcentration shiftedE_rev to about +4and +60 mV, respectively, and decreasedF_in amplitude,indicating thatF_in was carriedby Cl.F_in had an onsetdelay of ~400 ms, measured by application of a brief jet of ATP froma micropipette positioned near the follicle (50 µm).F_in was inhibitedby 50% in follicles pretreated with pertussis toxin. This suggests a Gprotein-mediated receptor channel pathway.F_in was mimickedby 2-MeSATP and UTP, the potency order (half-maximal effectiveconcentration) was 2-MeSATP (194 nM) > UTP (454 nM) > ATP(1,086 nM). All agonists generatedCl currents and displayedcross-inhibition on the others.F_in activation byacetylcholine also cross-inhibitedF_in-ATPresponses, suggesting that all act on a common channel-activationpathway.