Functional and molecular expression of volume‐regulated chloride channels in canine vascular smooth muscle cells

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Abstract
1 We examined the possibility of functional and molecular expression of volume‐regulated Cl− channels in vascular smooth muscle using the whole‐cell patch‐clamp technique and quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR) on cells from canine pulmonary and renal arteries. 2 Decreasing external osmolarity induced cell swelling, which was accompanied by activation of Cl−‐dependent outward‐rectifying membrane currents with an anion permeability sequence of SCN− > I− > Br− > Cl− > aspartate−. These currents were sensitive to block by DIDS, extracellular ATP and the antioestrogen compound tamoxifen. 3 Experiments were performed to determine whether the molecular form of the volume‐regulated chloride channel (ClC‐3) is expressed in pulmonary and renal arteries. Quantitative RT‐PCR confirmed expression of ClC‐3 in both types of smooth muscle. ClC‐3 expression was 76.4 % of β‐actin in renal artery and 48.0 % of β‐actin in pulmonary artery. 4 We conclude that volume‐regulated Cl− channels are expressed in vascular smooth muscle cells and exhibit functional properties similar to those found in other types of cells, presumably contributing to the regulation of cell volume, electrical activity and, possibly, myogenic tone.