Purine and pyrimidine nucleotide receptors in the apical membranes of equine cultured epithelia

1 The short circuit current (I-SC) technique was used to quantify electrolyte transport by equine cultured sweat gland epithelia. Adenosine 5'-triphosphate (ATP) and certain related compounds, caused transient increases in Ise when added to the apical solution. The order of potency was uridine triphosphate (UTP)>ATP>ADP>>AMP=adenosine. 2 The responses to apical nucleotides were due to chloride and bicarbonate secretion and were reduced in pertussis toxin-treated cells. P-2-receptors sensitive to uridine 5'-triphosphate (UTP, that interact with inhibitory G proteins. therefore appear to be present in the apical membrane. 3 Responses to ATP and UTP were reduced in cells loaded with BAPTA, a calcium chelator. BAPTA attenuated the response to ATP more than the response to UTP suggesting that these nucleotides may not act via a common pathway. 4 Cross-desensitization experiments indicated that two populations of UTP-sensitive receptor were present. One was sensitive to UTP and ATP, whereas the second was sensitive only to UTP. Uridine diphosphate appeared to activate the ATP-insensitive receptor population selectively. 5 These data suggest that apical pyrimidinoceptors may be expressed by these cells. The physiological role of these receptors is unknown but they may allow the autocrine regulation of epithelial function.