Alpha-adrenergic control of volume-regulated Cl- currents in rabbit atrial myocytes. Characterization of a novel ionic regulatory mechanism.
alpha-Adrenergic stimulation is known to play a role in cardiac arrhythmogenesis and to modulate a variety of cardiac K+ currents. The effects of alpha-adrenergic stimulation on Cl- currents are largely unknown. Many cardiac cell types show a volume-sensitive Cl- current induced by cell swelling (ICl.swell). The present experiments were designed to assess the potential alpha-adrenergic modulation of ICl.swell in rabbit atrial myocytes. ICl.swell was induced with the use of a hypotonic superfusate, under conditions designed to prevent currents carried by K+, Na+, and Ca2+ ions. A basal Cl- current (ICl.b) was observed under isotonic conditions in 128 of 150 cells (85%), had the same dependency on [Cl-]o as ICl.swell, and was reduced by cell shrinkage induced by hypertonic superfusion, suggesting that ICl.b is carried by the same volume-sensitive Cl- conductance as ICl.swell. Phenylephrine produced a concentration-dependent and near-complete inhibition of ICl.b and ICl.swell, with EC50 values of 86 +/- 5 and 72 +/- 7 (mean +/- SEM) mumol/L, respectively, at +20 mV. Norepinephrine (administered in the presence of 1 mumol/L propranolol) also inhibited ICl.b and ICl.swell, with EC50 values of 2.6 +/- 0.1 and 2.8 +/- 0.4 mumol/L, respectively. The concentration-response curve for phenylephrine was shifted significantly (P < .001) to the right by the alpha 1-adrenoceptor antagonist prazosin and by the alpha 1A-receptor antagonists (+)-niguldipine and 5-methylurapidil but was unaltered by the alpha 1B-receptor antagonist chloroethylclonidine (100 mumol/L). Inhibition of protein kinase C (PKC) with staurosporine, H-7, or 18-hour preincubation with the phorbol ester 4 beta-phorbol 12-myristate 13-acetate (PMA, 500 nmol/L) blocked the effects of phenylephrine on ICl.swell, and the highly selective PKC inhibitor bisindolylmaleimide blocked the effects of norepinephrine on ICl.swell and ICl.b. Both PMA and 1-oleoyl-2-acetylglycerol inhibited ICl.swell in a concentration-dependent fashion. In blinded studies, the phorbol ester phorbol 12,13-didecanoate (PDD) reduced ICl.swell by 91 +/- 3%; its inactive analogue 4 alpha-PDD had no effect (mean change, 3 +/- 1%). Preincubation with pertussis toxin (PTX) prevented the actions of phenylephrine on ICl.swell, indicating a role for a PTX-sensitive guanine nucleotide-binding (G) protein. We conclude that alpha-adrenergic agonists inhibit volume-sensitive Cl- currents in rabbit atrial cells by interacting with an alpha 1A-adrenoceptor mechanism that is coupled to PKC via a PTX-sensitive G protein.(ABSTRACT TRUNCATED AT 400 WORDS)
Duan
D
D
Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada.
Fermini
B
B
Nattel
S
S
D000200:Action Potentials; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D016275:Atrial Function; D001341:Autonomic Nervous System / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D018118:Chloride Channels / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology; D004594:Electrophysiology; D006325:Heart Atria / Q000166:cytology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013268:Stimulation, Chemical
D000317:Adrenergic alpha-Antagonists; D000959:Antihypertensive Agents; D002121:Calcium Channel Blockers; D018118:Chloride Channels; D004095:Dihydropyridines; D007473:Ion Channels; D010879:Piperazines; D011942:Receptors, Adrenergic, alpha; C057446:5-methylurapidil; D010656:Phenylephrine; D011493:Protein Kinase C; D009638:Norepinephrine; D011224:Prazosin; C054074:niguldipine