Evidence that outwardly rectifying Cl- channels underlie volume-regulated Cl- currents in heart.
Swelling-induced Cl- current (ICl.swell) is present in most cardiac tissues, but the unitary channel underlying ICls.well is unknown. We used the cell-attached patch-clamp technique to assess the properties of single channels underlying ICls.well and the basally active Cl- current (ICl.b) in rabbit atrial myocytes. Under isotonic conditions, single outwardly rectifying Cl- channels (ORCCs) with a slope conductance of 28 +/- 1 pS at the reversal potential were observed in 21 (5.7%) of 367 patches. Unconditional kinetic analysis revealed at least three open and four closed-channel states. Hypotonic superfusion-induced swelling resulted in the appearance of active channels in 41 (15.5%) of 265 patches without channel activity under isotonic conditions and caused a second active channel to appear in 3 of 14 patches showing a single channel under isotonic conditions. Overall, channels were seen in 54 of 336 patches under hypotonic conditions (16.1%, P < .001 versus isotonic conditions). The current-voltage relations, reversal potential-[Cl-]o relations, open probability, and kinetics of swelling-induced channels were indistinguishable from those of ORCCs under isotonic conditions. Unitary ORCCs, ICl.b, and ICl.swell were strongly and similarly inhibited by tamoxifen. Swelling-induced increases in macroscopic Cl- current were attributable to an increase in the number of active ORCCs with no significant effects on single-channel amplitude or open probability. Estimated macroscopic currents based on cell surface area, patch dimensions, single-channel ORCC current amplitude, open probability, and density were consistent with measured values of ICl.b and ICl.swell. We conclude that ORCCs underlie volume-regulated basal and swelling-induced Cl- currents in isolated rabbit atrial myocytes.
Duan
D
D
Department of Pharmacology and Therapeutics, McGill University, Montreal, Canada.
Hume
J R
JR
Nattel
S
S
D000818:Animals; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D002712:Chlorides / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D004965:Estrogen Antagonists / Q000494:pharmacology; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D007038:Hypotonic Solutions / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology; D011817:Rabbits; D013629:Tamoxifen / Q000494:pharmacology
D018118:Chloride Channels; D002712:Chlorides; D004965:Estrogen Antagonists; D007038:Hypotonic Solutions; D013629:Tamoxifen