Related Experiment Videos
Effect of chloride channel blockers on the cardiac CFTR chloride and L-type calcium currents
1Department of Pharmacology, University of South Carolina, School of Medicine, Columbia 29208, USA.
Objectives:
The aim of this study was to determine the effects of Cl- channel blockers on the cardiac cystic fibrosis transmembrane conductance regulator (CFTR) Cl- current (ICl) and the protein kinase A-regulated L-type calcium current (PKA-ICa).
Methods:
Whole-cell ICl and ICa were recorded from isolated guinea pig ventricular myocytes using the patch clamp technique during stimulation of PKA by forskolin (1 or 2 microM).
Results:
The inhibitory effects of clofibric acid, p-chlorophenoxy propionic acid, gemfibrozil, diphenylamine-2-carboxylate (DPC), anthracene-9-carboxylate, 4,4'dinitrostilbene-2,2'-disulfonic acid and indanyloxyacetic acid 94 were examined on the two currents. Clofibric acid (1 mM), p-chlorophenoxy propionic acid (1 mM) and gemfibrozil (250 microM) produced an approximate 50% decrease in ICl, but had no effect on the PKA-ICa. Surprisingly, application of DPC (500 microM and 1 mM) and anthracene-9-carboxylate (500 microM) strongly reduced both currents. However, inhibition of the Ca2+ and Cl- channels by DPC could be differentiated in two important ways. First, increasing the pH of the external solution from 7.4 to 10.0 prevented the block of ICl by DPC, but did not attenuate the reduction in the PKA-ICa. Second, DPC inhibited the PKA-ICa in mouse atrial myocytes which lacked ICl. Neither 4,4'dinitrostilbene-2,2'-disulfonic acid (100 microM) nor indanyloxyacetic acid 94 (50 microM) caused any change in either of the guinea pig ventricular currents.
Conclusions:
Drugs such as DPC and anthracene-9-carboxylate which block the cardiac CFTR Cl- channel also inhibit the regulation of the L-type ICa. During beta-adrenergic stimulation, changes produced by these drugs on the cardiac action potential duration will be attributable to inhibition of both the Cl- and Ca2+ currents. Analogues of clofibric acid may serve as selective blockers of the CFTR Cl- channel that can be used to determine the physiological function of ICl in cardiac excitation.
Insights
Certain channel blockers inhibit cardiac cystic fibrosis transmembrane conductance regulator (CFTR) chloride currents and affect calcium currents. Clofibric acid analogs may selectively block CFTR, aiding research into cardiac excitation.
Area of Science:
- Cardiovascular Physiology
- Ion Channel Pharmacology
- Molecular Cardiology
Background:
- The cardiac cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel plays a role in cardiac electrophysiology.
- Protein kinase A (PKA) regulates L-type calcium channels (ICa) in the heart.
Purpose of the Study:
- To investigate the effects of various chloride (Cl-) channel blockers on cardiac CFTR Cl- current (ICl) and PKA-regulated L-type calcium current (PKA-ICa).
- To differentiate the actions of specific blockers on distinct ion currents.
Main Methods:
- Whole-cell patch clamp recordings were performed on isolated guinea pig ventricular myocytes.
- Forskolin was used to stimulate PKA and modulate ion currents.
- The effects of clofibric acid, p-chlorophenoxy propionic acid, gemfibrozil, diphenylamine-2-carboxylate (DPC), and anthracene-9-carboxylate were assessed.
Main Results:
- Clofibric acid, p-chlorophenoxy propionic acid, and gemfibrozil reduced ICl by approximately 50% without affecting PKA-ICa.
- Diphenylamine-2-carboxylate (DPC) and anthracene-9-carboxylate significantly reduced both ICl and PKA-ICa.
- External solution pH modulation and experiments on mouse atrial myocytes distinguished DPC's effects on Cl- versus Ca2+ channels.
Conclusions:
- Drugs like DPC and anthracene-9-carboxylate inhibit both cardiac CFTR Cl- channels and L-type ICa regulation.
- These blockers influence cardiac action potential duration during beta-adrenergic stimulation by affecting both Cl- and Ca2+ currents.
- Analogues of clofibric acid show potential as selective CFTR blockers for studying ICl's physiological role in cardiac excitation.