Activation of Ca2+-dependent K+ and Cl? currents by UTP and ATP in CFPAC-1 cells

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Abstract
Activation of Cl− and K+ conductances by nucleotide receptor-operated mobilization of intracellular Ca2+ was investigated in CFPAC-1 cells with the perforated-patch technique. Adenosine 5′-triphosphate (ATP) and uridine 5′-triphosphate (UTP) caused a dose-dependent fast and transient membrane hyperpolarization. UTP was more effective than ATP. In voltageclamped cells, two currents with different ionic permeability and kinetics were activated by the nucleotides. The first one was carried by Cl− ions, peaked in the first few seconds after addition of nucleotides, and lasted for 1±0.3 min. Its amplitude was about 2.7 nA at −100 mV with 100 μmol/l of either ATP or UTP. The second current was carried by K+ ions and was blocked by Cs+. This current peaked more slowly and had a mean duration of 4.6±0.7 min. Its amplitude was 0.9 nA and 0.5 nA at −20 mV with 100 umol/l UTP and ATP, respectively. Activation of the nucleotide receptor caused a transient increase in intracellular Ca2+ concentration ([Ca2+]i) that was similar in the presence or absence of extracellular Ca2+. The ED50 for UTP was 24 umol/l and that for ATP was 94 μmol/l. Depletion of the inositol 1,4,5-trisphosphate-sensitive Ca2+ store by thapsigargin prevented both the nucleotide-induced [Ca2+]i increase and the activation of membrane currents. Addition of 2 mmol/l Ca2+ to thapsigargin-treated cells produced a sustained increase of Cl− and K+ currents, which was reversed by Ca2+ removal. The present study demonstrates that CFPAC-1 cells respond to nucleotide receptor activation with a transient increase in [Ca2+]i that stimulates Ca2+-dependent Cl− and K+ currents. This phenomenon is probably mediated by inositol 1,4,5-trisphosphate-dependent Ca2+ stores.