Coupling of a P2Z-like purinoceptor to a fatty acid-activated K+ channel in toad gastric smooth muscle cells

1. Extracellular application of ATP generates two whole-cell currents in to ad gastric smooth muscle cells: an immediate inward non-selective cation cu rrent (due to the activation of a P2X or P2Z-like receptor) and a slowly de veloping outward K+ current. The inward non-selective cation current depend s on the continuous presence of ATP while the outward K+ current can last f or minutes after ATP application ceases. 2. In cell-attached patches, application of ATP to the extra-patch membrane can activate K+ channels in the patch indicating that a diffusible cellula r messenger may be involved. The characteristics of these K+ channels are s imilar to those of a previously described fatty acid-activated K+ channel t hat is also a stretch-activated channel. 3. This whole-cell K+ current can be induced by ATP in the absence of extra cellular Ca2+ (with EGTA present to chelate trace amounts). However, the cu rrent generated in the presence of extracellular Ca2+ is considerably large r. 4. The pharmacological profiles for the activation of the non-selective cat ion current and the K+ current are similar, suggesting that the same P2Z-li ke receptor could be mediating both responses. This type of plasma membrane receptor/channel-channel coupling by a process that does not appear to inv olve Ca2+ flow through the receptor/channel or a subsequent membrane potent ial change may be representative of a new class of signalling mechanisms.