A Ca(2+)-activated Cl- current in sheep parotid secretory cells.
Previous studies have shown that the whole-cell current-voltage (I-V) relation of unstimulated sheep parotid cells is dominated by two K+ conductances, one outwardly and the other inwardly rectifying. We now show that once these K+ conductances are blocked by replacement of pipette K+ with Na+ and by the addition of 5 mmol/liter CsCl to the bath, there remains an outwardly rectifying conductance with a reversal potential of 0 mV. Replacement of 120 mmol/liter NaCl in the pipette solution with an equimolar amount of Na-glutamate shifted the reversal potential of this residual current to -55 mV, indicating that the conductance was Cl- selective. The Cl- current was activated by increasing the free Ca2+ in the pipette solution from 10 to 100 nmol/liter. When the Ca2+ concentration in the pipette solution was 10 nmol/liter, the relaxations observed in response to membrane depolarization could be fitted with a single exponential, whose time constant increased from 81 to 183 ms as the pipette potential was increased from -30 to +60 mV. Relaxation analysis showed that the current was activated by membrane depolarization. Reversal potential measurements in experiments in which external Cl- was replaced with various anions, gave the following relative permeabilities: SCN- (1.80) > I- (1.09) > Cl- (1) > NO3- (0.92) > Br- (0.75). The relative conductances were: SCN- (2.18) > I- (1.07) > Cl- (1.00) > Br- (0.91) > NO3- (0.50). The Cl- current was blocked by NPPB (ID50 approximately 10 microM), DIDS (10 or 30 mumol/liter) and furosemide (100 mumol/liter).
Ishikawa
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Department of Physiology, University of Sydney, N.S.W., Australia.
Cook
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D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D002463:Cell Membrane Permeability / Q000502:physiology; D002478:Cells, Cultured; D018118:Chloride Channels / Q000032:analysis / Q000502:physiology*; D002712:Chlorides / Q000493:pharmacokinetics; D004305:Dose-Response Relationship, Drug; D005665:Furosemide / Q000494:pharmacology; D007455:Iodine / Q000493:pharmacokinetics; D008564:Membrane Potentials / Q000502:physiology; D009566:Nitrates / Q000493:pharmacokinetics; D009579:Nitrobenzoates / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D011188:Potassium / Q000493:pharmacokinetics; D015221:Potassium Channels / Q000032:analysis / Q000502:physiology; D012756:Sheep / Q000502:physiology*; D012964:Sodium / Q000493:pharmacokinetics
D018118:Chloride Channels; D002712:Chlorides; D009566:Nitrates; D009579:Nitrobenzoates; D015221:Potassium Channels; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D005665:Furosemide; D007455:Iodine; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium; D002118:Calcium