Effect of chloride channel blockers on the cardiac CFTR chloride and L-type calcium currents.
OBJECTIVE
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.
Walsh
K B
KB
Department of Pharmacology, University of South Carolina, School of Medicine, Columbia 29208, USA.
Wang
C
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D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D018118:Chloride Channels / Q000187:drug effects*; D002712:Chlorides / Q000378:metabolism; D002995:Clofibric Acid / Q000494:pharmacology*; D005576:Colforsin / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D011345:Fenofibrate / Q000031:analogs & derivatives / Q000494:pharmacology; D015248:Gemfibrozil / Q000494:pharmacology; D006016:Glycolates / Q000494:pharmacology; D006168:Guinea Pigs; D017136:Ion Transport / Q000187:drug effects; D051379:Mice; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D013267:Stilbenes / Q000494:pharmacology; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D000873:Anthracenes; D002121:Calcium Channel Blockers; D018118:Chloride Channels; D002712:Chlorides; D006016:Glycolates; D013267:Stilbenes; D062367:ortho-Aminobenzoates; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D002995:Clofibric Acid; C015765:MK 473; C022306:4,4'-dinitro-2,2'-stilbenedisulfonic acid; C010030:9-anthroic acid; C001209:fenamic acid; C006012:fenofibric acid; D015248:Gemfibrozil; D002118:Calcium; D011345:Fenofibrate