CL- CURRENTS ACTIVATED VIA PURINERGIC RECEPTORS IN XENOPUS FOLLICLES

Ionic currents elicited via purinergic receptors located in the membra ne of Xenopus follicles were studied using electrophysiological techni ques. Follicles responded to ATP-activating inward currents with a fas t time course (F-in). In Ringer solution, reversal potential (E-rev) o f 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- concen tration shifted E-rev to about +4 and +60 mV, respectively, and decrea sed 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 brie f jet of ATP from a micropipette positioned near the follicle (50 mu m ). F-in was inhibited by 50% in follicles pretreated with pertussis to xin. This suggests a CT protein-mediated receptor channel pathway. F-i n was mimicked by 2-MeSATP and UTP, the potency order (half-maximal ef fective concentration) was 2-MeSATP (194 nM) > UTP (454 nM) > ATP (1,0 86 nM). All agonists generated Cl- currents and displayed cross-inhibi tion on the others. F-in activation by acetylcholine also cross-inhibi ted F-in-ATP responses, suggesting that all act on a common channel-ac tivation pathway.