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

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Abstract
1 Extracellular application of ATP generates two whole-cell currents in toad gastric smooth muscle cells: an immediate inward non-selective cation current (due to the activation of a P2X or P2Z-like receptor) and a slowly developing outward K+ current. The inward non-selective cation current depends on the continuous presence of ATP while the outward K+ current can last for 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 cellular messenger may be involved. The characteristics of these K+ channels are similar to those of a previously described fatty acid-activated K+ channel that is also a stretch-activated channel. 3 This whole-cell K+ current can be induced by ATP in the absence of extracellular Ca2+ (with EGTA present to chelate trace amounts). However, the current generated in the presence of extracellular Ca2+ is considerably larger. 4 The pharmacological profiles for the activation of the non-selective cation current and the K+ current are similar, suggesting that the same P2Z-like receptor could be mediating both responses. This type of plasma membrane receptor/channel-channel coupling by a process that does not appear to involve Ca2+ flow through the receptor/channel or a subsequent membrane potential change may be representative of a new class of signalling mechanisms.
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