PHARMACOLOGICAL PROPERTIES OF THE SWELLING-INDUCED CHLORIDE CURRENT OF DOG ATRIAL MYOCYTES

Introduction: Swelling induced chloride currents may contribute to cardiac electrical activity and cell volume regulation, Identification of selective blockers would aid in understanding the functional contribution(s) of this current. Methods and Results: Dog atrial cells were used to investigate the pharmacologic properties of the swelling-induced chloride current. Whole cell patch clamp was used. Swelling-induced chloride current was activated by osmotic stress. Initially, the chloride selectivity and calcium independence of the swelling-induced current in dog atrial cells was demonstrated. Subsequently, a number of putative chloride channel blockers were examined, Anthracene-9-carboxylic acid (1 mM) and dideoxyforskolin (100 mu M) and extracellular cAMP (5 mM) were found to partially inhibit the swelling-induced chloride current (similar to 50%, 80%, and 10% inhibition, respectively); Niflumic acid (100 mu M), nitrophenylpropylamino benzoate (NPPB; 10 to 40 mu M), and (+) 2-[(2-cyclopentyl-6,7- dichloro-2,3-dihydro-2-methyl-1-oxy-1H-inden-5-yl)oxy] acetic acid (indanyloxyacetic acid; IAA-94; 100 mu M) could fully inhibit the swelling-induced chloride current without decreasing cell size, DIDS (100 mu M) and dinitrostilbene disulfonic acid (DMDS; 5 mM) fully inhibited outward currents but only partially inhibited inward current. Conclusions: Niflumic acid, IAA-94, and NPPB were identified as full blockers of cardiac swelling-induced chloride current. Nonspecific effects were identified for each of the full blockers. Experiments that use these agents as functional antagonists should be carefully designed and interpreted with caution.