Separate Cl- conductances activated by cAMP and Ca2+ in Cl(-)-secreting epithelial cells.
We studied the cAMP- and Ca2(+)-activated secretory Cl- conductances in the Cl(-)-secreting colonic epithelial cell line T84 using the whole-cell patch-clamp technique. Cl- and K+ currents were measured under voltage clamp. Forskolin or cAMP increased Cl- current 2-15 times with no change in K+ current. The current-voltage relation for cAMP-activated Cl- current was linear from -100 to +100 mV and showed no time-dependent changes in current during voltage pulses. Ca2+ ionophores or increased pipette Ca2+ increased both Cl- and K+ currents 2-30 times. The Ca2(+)-activated Cl- current was outwardly rectified, activated during depolarizing voltage pulses, and inactivated during hyperpolarizing voltage pulses. Addition of ionophore after forskolin further increased Cl- conductance 1.5-5 times, and the current took on the time-dependent characteristics of that stimulated by Ca2+. Thus, cAMP and Ca2+ activate Cl- conductances with different properties, implying that these second messengers activate different Cl- channels or that they induce different conductive and kinetic states in the same Cl- channel.
Cliff
W H
WH
Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
Frizzell
R A
RA
D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D004553:Electric Conductivity; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008536:Meglumine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D013873:Thionucleotides / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000502:physiology
D002712:Chlorides; D013873:Thionucleotides; D005576:Colforsin; D000001:Calcimycin; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D015759:Ionomycin; D008536:Meglumine; D000242:Cyclic AMP; D002118:Calcium