Purinoceptors Evoke Different Electrophysiological Responses in Pancreatic Ducts

Abstract

In epithelia, extracellular nucleotides are often asso- ciated with regulation of ion transporters, especially Cl channels. In this study, we investigated which puri- noceptors are present in native pancreatic ducts and how they regulate ion transport. We applied whole-cell patch-clamp recordings, intracellular Ca2 and pH measurements, and reverse transcription-polymerase chain reaction (RT-PCR) analysis. The data show two types of purinoceptors and cellular responses. UTP and ATP produced large Ca2 transients, a decrease in in- tracellular pH, 8–10-mV depolarization of the membrane voltage, and a decrease in the whole-cell conductance. The membrane effects were due to closure of K chan- nels, as confirmed by dependence on extracellular K. UTP/ATP effects could be associated with P2Y2 purino- ceptors, and RT-PCR revealedmRNAsfor P2Y2 and P2Y4 receptors. On the other hand, 2,3-O-4-benzoylbenzoyl- ATP induced Ca2 influx and 20-mV depolarization of the membrane voltage with a concomitant increase in the whole-cell conductance. These effects were depend- ent on extracellular Na, not Cl, indicating opening of cation channels associated with P2X7 purinoceptors. RT-PCR showed mRNAs for P2X7 and P2X4 receptors. In microperfused ducts, luminal (but not basolateral) ATP caused large depolarizations of membrane voltages re- corded with microelectrodes, consistent with luminal localization of P2X7 receptors. Thus, P2Y2 (and possibly P2Y4) purinoceptors inhibit K channels and may not support secretion in native ducts. P2X7 (and possibly P2X4) receptors are associated with cation channels and may contribute to regulation of secretion. Extracellular nucleotides are regulators of a wi