New selective inhibitors of calcium‐activated chloride channels – T16Ainh‐A01, CaCCinh‐A01 and MONNA – what do they inhibit?

• Published in: British journal of pharmacology 2015-08, Vol.172 (16), p.4158-4172
• Main Authors: Boedtkjer, D M B, Kim, S, Jensen, A B, Matchkov, V M, Andersson, K E
• Format: Article
• Language: English
• Subjects: Research Papers
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/bph.13201

Background and Purpose T16Ainh‐A01, CaCCinh‐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 T16Ainh‐A01 (0.1–10 μM): IC50 and maximum relaxation were equivalent in ±chloride (30 min aspartate substitution) and the T16Ainh‐A01‐induced vasorelaxation ±chloride were accompanied by membrane hyperpolarization and lowering of intracellular calcium. However, agonist concentration–response curves ±chloride, with 10 μM T16Ainh‐A01 present, achieved similar maximum constrictions although agonist‐sensitivity decreased. Contractions induced by elevated extracellular potassium were concentration‐dependently relaxed by T16Ainh‐A01 ±chloride. Moreover, T16Ainh‐A01 inhibited VDCCs in A7r5 cells in a concentration‐dependent manner. CaCCinh‐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 T16Ainh‐A01, CaCCinh‐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.