Activation of volume‐regulated chloride currents by reduction of intracellular ionic strength in bovine endothelial cells

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Abstract
1 We have studied the effects of intracellular ionic strength (Γi) on the swelling-activated whole-cell Cl− current (ICl,swell) in cultured calf pulmonary artery endothelial cells (CPAE cells). 2 Reducing Γi from 155 to 95 mM at constant osmolarity and Cl− concentration activates an outwardly rectifying current that is mainly carried by Cl− ions and inactivates at positive potentials. The amplitude of the current is larger at more reduced levels of Γi. 3 The permeability ratio for the anions I−, Br−, Cl− and gluconate (PI: PBr: PCl: Pgluc) was 1.35 : 1.03 : 1 : 0.17. 3 Blockers of the swelling-activated Cl− current in CPAE cells also inhibit the current which is activated by a reduction in Γi with an IC50 of 1.1 μM for tamoxifen, 1.3 μM for mibefradil, and 35 μM for quinidine. 4 The protein tyrosine kinase inhibitors tyrphostin B46 (50 μM) and genistein (100 μM), which inhibit ICl,swell in CPAE cells, also inhibited the Γi-induced current by 92.9 ± 2.4% (n= 3) and 41.2 ± 5.0% (n= 4), respectively. 5 Hypertonic extracellular solutions rapidly and reversibly antagonized the Γi-activated current, whereas increasing Γi from 155 to 195 mM precluded activation of ICl,swell by hypotonic shock. 6 It is concluded that a reduction of Γi activates an anion current that is identical to that activated by cell swelling. Changes in intracellular ionic strength may shift the volume set point for activation of ICl, swell.