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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
Susanne E.
Hede,
Jan
Amstrup,
Bettina C.
Christoffersen, and
Ivana
Novak
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.
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 1999 by the American Society for Biochemistry and Molecular Biology.
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