ACTIVATION OF APICAL P-2U PURINE RECEPTORS PERMITS INHIBITION OF ADRENALINE-EVOKED CYCLIC-AMP ACCUMULATION IN CULTURED EQUINE SWEAT GLAND EPITHELIAL-CELLS

Experiments were undertaken using cultured equine sweat gland epitheli al cells that express purine receptors belonging to the P-2U subclass which allow the selective agonist uridine triphosphate (UTP) to increa se the concentration of intracellular free Ca2+ ([Ca2+](i)). Experimen ts using pertussis toxin (Ptx), which inactivates certain guanine-nucl eotide-binding proteins (G-proteins), showed that this response consis ted of Ptx-sensitive and Ptx-resistant components, and immunochemical analyses of the G-protein a subunits present in the cells showed that both Ptx-sensitive (alpha i1-3) and Ptx-resistant (alpha q/11) G-prote ins were expressed, P-2U receptors may, therefore, normally activate b oth of these G-protein families, Ptx-sensitive, alpha i2/3 subunits pe rmit inhibitory control of adenylate cyclase, and UTP was shown to cau se Ptx-sensitive inhibition of adrenaline-evoked cyclic AMP accumulati on, suggesting that the receptors activate G(i2/3). Experiments using cells grown on permeable supports suggested that P-2U receptors became essentially confined to the apical membrane in post-confluent culture s, Polarised epithelia may, therefore, express apical P-2U receptors w hich influence two centrally important signal transduction pathways, I t is highly improbable that these receptors could be activated by nucl eotides released from purinergic nerves, but they may be involved in t he autocrine regulation of epithelial function.