ACTIVATION OF CA2+-DEPENDENT K+ AND CL- CURRENTS BY UTP AND ATP IN CFPAC-1 CELLS

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 voltage-clamped 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 mu mol/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 mu mol/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 ED(50) for UTP was 24 mu mol/l and that for ATP was 94 mu mol/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.