Dynamics of Ca²⁺-Dependent Cl^- Channel Modulation by Niflumic Acid in Rabbit Coronary Arterial Myocytes

Abstract

Calcium-activated chloride channels (Cl Ca ) 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 Cl Ca in vascular myocytes, was shown recently to cause inhibition and paradoxical stimulation of sustained calcium-activated chloride currents [I Cl(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 I Cl(Ca) evoked by intracellular Ca 2ϩ clamped at 500 nM were dose-dependently inhibited by NFA (IC 50 ϭ 159 M) and transiently augmented in a concentration-independent manner (10 M to 1 mM) ϳ2-fold after NFA removal. However, the time to peak and duration of NFAenhanced I Cl(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

Angiotensin II-stimulated Ca2+ entry mechanisms in afferent arterioles: role of transient receptor potential canonical channels and reverse Na+/Ca2+ exchange

“…Lower concentrations of NFA block the Cl Ca channel, whereas higher concentrations (Ն50 M) also stimulate the Ca 2ϩ -activated K ϩ (KCa) channel (21,31,41,42). Ryanodine (100 M) and TMB-8 (10 M) block the RyR and IP3R, respectively (13).…”

“…NFA has been considered to be among the most potent blockers of Cl Ca channels and therefore has been widely used to assess their role in the control of vascular tone (22, 31). As noted above, NFA inhibits the channels at low concentrations (Յ10 M) and activates the channels at higher concentrations (Ն50 M) and after prolonged (minutes) exposure (25,31). We studied two concentrations of NFA, 10 and 50 M.…”

Transport and Function of Chloride in Vascular Smooth Muscles

“…This has been achieved by agonist stimulation [101,102], membrane permeabilization [18,103], stimulation of Ca 2+ release [104,105,106] and Ca 2+ influx [104,106,107,108,109,110], as well as by direct loading of Ca 2+ from the pipette [111,112,113,114,115] or by manipulation of the solutions under single channel recordings [116,117,118,119]. The I Cl(Ca) has been characterized by several common features [1,67,120,121,122] (fig.…”

Direct Regulation of BK Channels by Phosphatidylinositol 4,5-Bisphosphate as a Novel Signaling Pathway

“…We used perforated patches to keep the intracellular milieu intact and recorded total outward currents in PSS containing 0.1 mM nifl umic acid to block Ca 2+ -activated Cl Ϫ channels ( Ledoux et al, 2005 ) and 5 mM 4-aminopyridine to block voltage-gated K + channels other than BK ( Thebaud et al, 2004 ). Under these conditions, myocytes displayed noninactivating outward currents (e.g., 483 pA peak amplitude at 100 mV; Fig.…”