Properties of single outwardly rectifying Cl- channels in heart.
A variety of potentially important macroscopic Cl- currents have been described in the heart. Although the single-channel properties of the cAMP-dependent current (ICl.cAMP) have been well described, the single-channel equivalents of the other forms of cardiac Cl- current remain unknown. Unlike ICl.cAMP, many of these currents show prominent outward rectification in the presence of symmetrical transmembrane Cl- gradients and sensitivity to disulfonic stilbene Cl- transport blockers. We used the patch-clamp technique to search for single Cl- channels in inside-out patches from rabbit atrial cell membranes, under conditions minimizing the chances of observing channels carrying Na+, Ca2+, or K+. Under symmetrical Cl- conditions, single-channel activity was seen in 14 (9%) of 155 patches. Channels showed strong outward rectification and a unitary conductance of 60 +/- 3 picosiemens (mean +/- SEM) at positive voltages. The current-voltage relation was not altered by replacement of cations by the impermeant cation N'-methyl-D-glucamine (NMDG) and shifted as expected for a Cl(-)-selective channel when methanesulfonate was substituted for Cl-. The Cl- transport blockers DIDS (diisothiocyanatostilbene-2,2'-disulfonic acid, 100 mumol/L) and SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid, 1 mmol/L) strongly and reversibly inhibited channel activity when added to the bath and caused channel flickering suggesting open-channel block. Ensemble-average currents showed no time dependence, and the form of the ensemble-average current-voltage relation was similar to that of macroscopic background Cl- current.(ABSTRACT TRUNCATED AT 250 WORDS)
Duan
D
D
Department of Medicine, Montreal Heart Institute, Quebec, Canada.
Nattel
S
S
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000503:physiopathology; D016275:Atrial Function; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D048429:Cell Size; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D004553:Electric Conductivity; D006321:Heart / Q000502:physiology*; D006325:Heart Atria / Q000166:cytology; D066298:In Vitro Techniques; D009206:Myocardium / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism / Q000502:physiology; D011817:Rabbits; D015222:Sodium Channels / Q000378:metabolism / Q000502:physiology; D013267:Stilbenes / Q000494:pharmacology
D015220:Calcium Channels; D018118:Chloride Channels; D015221:Potassium Channels; D015222:Sodium Channels; D013267:Stilbenes; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid