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J Biol Chem, Vol. 274, Issue 45, 31784-31791, November 5, 1999

Purinoceptors Evoke Different Electrophysiological Responses in Pancreatic Ducts
P2Y INHIBITS K⁺ CONDUCTANCE, AND P2X STIMULATES CATION CONDUCTANCE

From the August Krogh Institute, Copenhagen University, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark

In epithelia, extracellular nucleotides are often associated with regulation of ion transporters, especially Cl channels. In this study, we investigated which purinoceptors 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 intracellular 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⁺ channels, as confirmed by dependence on extracellular K⁺. UTP/ATP effects could be associated with P2Y₂ purinoceptors, and RT-PCR revealed mRNAs for 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 dependent 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 recorded 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.

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