ABSTRACT
BACKGROUND AND PURPOSE: T16A(inh)-A01, CaCC(inh)-A01 and MONNA are identified as selective inhibitors of the TMEM16A calcium-activated chloride channel (CaCC). The aim of this study was to examine the chloride-specificity of these compounds on isolated resistance arteries in the presence and absence (±) of extracellular chloride. EXPERIMENTAL APPROACH: Isolated resistance arteries were maintained in a myograph and tension recorded, in some instances combined with microelectrode impalement for membrane potential measurements or intracellular calcium monitoring using fura-2. Voltage-dependent calcium currents (VDCC) were measured in A7r5 cells with voltage-clamp electrophysiology using barium as a charge carrier. KEY RESULTS: Rodent arteries preconstricted with noradrenaline or U46619 were concentration-dependently relaxed by T16A(inh) -A01 (0.1-10 µM): IC50 and maximum relaxation were equivalent in ±chloride (30 min aspartate substitution) and the T16A(inh) -A01-induced vasorelaxation ±chloride were accompanied by membrane hyperpolarization and lowering of intracellular calcium. However, agonist concentration-response curves ±chloride, with 10 µM T16A(inh) -A01 present, achieved similar maximum constrictions although agonist-sensitivity decreased. Contractions induced by elevated extracellular potassium were concentration-dependently relaxed by T16A(inh)-A01 ±chloride. Moreover, T16A(inh) -A01 inhibited VDCCs in A7r5 cells in a concentration-dependent manner. CaCC(inh) -A01 and MONNA (0.1-10 µM) induced vasorelaxation ±chloride and both compounds lowered maximum contractility. MONNA, 10 µM, induced substantial membrane hyperpolarization under resting conditions. CONCLUSIONS AND IMPLICATIONS: T16A(inh) -A01, CaCC(inh) -A01 and MONNA concentration-dependently relax rodent resistance arteries, but an equivalent vasorelaxation occurs when the transmembrane chloride gradient is abolished with an impermeant anion. These compounds therefore display poor selectivity for TMEM16A and inhibition of CaCC in vascular tissue in the concentration range that inhibits the isolated conductance.
Subject(s)
Chloride Channels/antagonists & inhibitors , Pyrimidines/pharmacology , Thiazoles/pharmacology , Thiophenes/pharmacology , Vasodilator Agents/pharmacology , ortho-Aminobenzoates/pharmacology , Animals , Cell Line , Cerebral Arteries/drug effects , Cerebral Arteries/physiology , Chloride Channels/physiology , Female , In Vitro Techniques , Male , Mesenteric Arteries/drug effects , Mesenteric Arteries/physiology , Mice, Inbred C57BL , Rats, WistarABSTRACT
This minireview discusses vasomotion, which is the oscillation in tone of blood vessels leading to flowmotion. We will briefly discuss the prevalence of vasomotion and its potential physiological and pathophysiological relevance. We will also discuss the models that have been suggested to explain how a coordinated oscillatory activity of the smooth muscle tone can occur and emphasize the role of the endothelium, the handling of intracellular Ca(2+) and the role of smooth muscle cell ion conductances. It is concluded that vasomotion is likely to enhance tissue dialysis, although this concept still requires more experimental verification, and that an understanding at the molecular level for the pathways leading to vasomotion is beginning to emerge.
Subject(s)
Endothelium, Vascular/physiology , Muscle, Smooth, Vascular/physiology , Vasomotor System/physiology , Animals , Calcium/metabolism , Calcium Signaling/physiology , Cell Communication/physiology , Chlorides/metabolism , Gap Junctions/metabolism , Humans , Membrane Potentials/physiology , Mesenteric Arteries/metabolism , Models, BiologicalABSTRACT
The possibility that Ca(2+)-activated Cl(-) conductances (CaCCs) contribute to oscillations in vascular tone (vasomotion) is tested in isolated mesenteric small arteries from rats where cGMP independent (I (Cl(Ca))) and cGMP-dependent (I (Cl(Ca,cGMP))) chloride conductances are important. The effect of anion substitution and Cl(-) channel blockers on noradrenaline (NA)-stimulated tension in isometrically mounted mesenteric arteries and for chloride conductance of smooth muscle cells isolated from these arteries were assessed electrophysiologically. Cl(-) (o) replacement with aspartate blocked vasomotion while 36mM SCN(-) (o) (substituted for Cl(-)) was sufficient to inhibit vasomotion. Oscillations in tone, membrane potential, and [Ca(2+)](i) disappeared with 36mM SCN(-). DIDS and Zn(2+) blocked I (Cl(Ca,cGMP)) but not I (Cl(Ca)). Vasomotion was not sensitive to DIDS and Zn(2+), and DIDS and Zn(2+) induce vasomotion in arteries without endothelium. The vasomotion in the presence of DIDS and Zn(2+) was sensitive to 36mM SCN(-) (o). The anion substitution data indicate that Cl(-) is crucial for the V (m) and [Ca(2+)](i) oscillations underlying vasomotion. The Cl(-) channel blocker data are consistent with both CaCCs being important.
