RT Journal Article
SR Electronic
T1 Dynamics of Ca<sup>2+</sup>-Dependent Cl<sup>-</sup> Channel Modulation by Niflumic Acid in Rabbit Coronary Arterial Myocytes
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 163
OP 173
DO 10.1124/mol.104.004168
VO 67
IS 1
A1 Jonathan Ledoux
A1 Iain A. Greenwood
A1 Normand Leblanc
YR 2005
UL http://molpharm.aspetjournals.org/content/67/1/163.abstract
AB Calcium-activated chloride channels (ClCa) are crucial regulators of vascular tone by promoting a depolarizing influence on the resting membrane potential of vascular smooth muscle cells. Niflumic acid (NFA), a potent blocker of ClCa in vascular myocytes, was shown recently to cause inhibition and paradoxical stimulation of sustained calcium-activated chloride currents [ICl(Ca)] in rabbit pulmonary artery myocytes. The aims of the present study were to investigate whether NFA produced a similar dual effect in coronary artery smooth muscle cells and to determine the concentration-dependence and dynamics of such a phenomenon. Sustained ICl(Ca) evoked by intracellular Ca2+ clamped at 500 nM were dose-dependently inhibited by NFA (IC50 = 159 μM) and transiently augmented in a concentration-independent manner (10 μM to 1 mM) ∼2-fold after NFA removal. However, the time to peak and duration of NFA-enhanced ICl(Ca) increased in a concentration-dependent fashion. Moreover, the rate of recovery was reduced by membrane depolarization, suggesting the involvement of a voltage-dependent step in the interaction of NFA, leading to stimulation of ICl(Ca). Computer simulations derived from a kinetic model involving low (Ki = 1.25 mM) and high (Ki &lt; 30 μM) affinity sites could reproduce the properties of the NFA-modulated ICl(Ca) fairly well.