Cl- currents activated via purinergic receptors in Xenopus follicles

Ionic currents elicited via purinergic receptors located in the membrane of Xenopus follicles were studied using electrophysiological techniques. Follicles responded to ATP-activating inward currents with a fast time course (F-in). In Ringer solution, reversal potential (E-rev) of F-in was -22 mV, which did not change with external substitutions of Na+ or K+, whereas solutions containing 50 or 5% of normal Cl- concentration shifted E-rev to about +4 and +60 mV, respectively, and decreased F-in amplitude, indicating that F-in was carried by Cl-. F-in had an onset delay of similar to 400 ms, measured by application of a brief jet of ATP from a micropipette positioned near the follicle (50 mu m). F-in was inhibited by 50% in follicles pretreated with pertussis toxin. This suggests a CT protein-mediated receptor channel pathway. F-in was mimicked by 2-MeSATP and UTP, the potency order (half-maximal effective concentration) was 2-MeSATP (194 nM) > UTP (454 nM) > ATP (1,086 nM). All agonists generated Cl- currents and displayed cross-inhibition on the others. F-in activation by acetylcholine also cross-inhibited F-in-ATP responses, suggesting that all act on a common channel-activation pathway.