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Chloride conductance regulated by cyclic AMP-dependent protein kinase in cardiac myocytes
A Bahinski1, A C Nairn, P Greengard
1Laboratory of Cardiac Physiology, Rockefeller University, New York 10021.
Abstract:
In heart cells, cyclic AMP-dependent protein kinase (PKA) regulates calcium- and potassium-ion current by phosphorylating the ion channels or closely associated regulatory proteins. We report here that isoprenaline induced large chloride-ion currents in voltage-clamped, internally-dialysed myocytes from guinea-pig ventricles. The Cl- current could be activated by intracellular dialysis with cAMP or the catalytic subunit of PKA, indicating regulation by phosphorylation. In approximately symmetrical solutions of high Cl- concentration, the macroscopic cardiac Cl- current showed little rectification, unlike the single-channel current in PKA-regulated Cl- channels of airway epithelial cells. But, like epithelial Cl- -channel currents, the cardiac Cl- current was sensitive to the distilbene,4,4'-dinitrostilbene-2,2'-disulphonic acid (DNDS). In the absence of kinase activation, cardiac sarcolemmal Cl- conductance was negligible. During beta-adrenergic stimulation of the heart, this novel Cl- conductance should accelerate action-potential repolarization and so protect impulse propagation in the face of the possibly arrhythmogenic increases in heart rate and in calcium entry into the cells.
Insights
Heart cells possess a novel chloride current regulated by cyclic AMP-dependent protein kinase (PKA). This finding reveals a new mechanism for controlling cardiac electrical activity during beta-adrenergic stimulation.
Area of Science:
- Cardiology
- Molecular Biology
- Ion Channel Physiology
Background:
- Cyclic AMP-dependent protein kinase (PKA) is known to regulate calcium and potassium ion currents in heart cells through phosphorylation.
- The role of chloride ion currents in cardiac electrophysiology, particularly under beta-adrenergic stimulation, remains less understood.
Purpose of the Study:
- To investigate the presence and regulation of chloride ion currents in guinea-pig ventricular myocytes.
- To determine if PKA modulates these chloride currents via phosphorylation.
Main Methods:
- Utilized voltage-clamped, internally-dialysed guinea-pig ventricular myocytes.
- Applied isoprenaline, cyclic AMP (cAMP), and the catalytic subunit of PKA to activate currents.
- Examined current properties including rectification and sensitivity to DNDS.
Main Results:
- Isoprenaline induced significant chloride currents in ventricular myocytes.
- These currents were activated by intracellular cAMP or PKA catalytic subunit, confirming PKA-mediated phosphorylation.
- The cardiac chloride current exhibited minimal rectification and was sensitive to DNDS, similar to epithelial chloride channels.
Conclusions:
- A novel, PKA-regulated chloride conductance exists in the cardiac sarcolemma.
- This conductance likely accelerates action potential repolarization during beta-adrenergic stimulation.
- This mechanism may protect against arrhythmias associated with increased heart rate and calcium entry.