Further characteristics of hyposmotically activated K loss in human lens epithelial cells (hLECs)

Abstract

Regulatory volume decrease of hLECs in hyposmotic (150 mOsM) media involves KCa3.1 (IK) channel activation and cell water loss. High external K and clotrimazole (CTZ), but not a variety of anion channel blockers, were inhibitory. Extending these findings, we studied the selective IK channel blocker (TRAM‐34 [1‐[(2‐chlorophenyl) diphenylmethyl]‐1H‐pyrazole]), and additional anion channel blockers used in other systems, especially DIOA {[(dihydro‐indenyl)oxy]alkanoic acid]}, phloretin and DCPIB [4‐2(butyl‐6,7‐dichloro‐2‐cyclopentylindan‐1‐on‐5‐yl)oxybutyric acid]. Ouabain‐ and bumetanide‐insensitive K loss and Rb influx were measured in hLECs (FHL124) by atomic absorption spectrophometry. TRAM‐34 (>50 μM) reduced K loss by ~ 30% with little effects on Rb influx, an asymmetry contrasting with the total inhibition of both fluxes by CTZ, also an inhibitor of P450, suggesting at least two different mechanisms either at the K channel and/or regulatory levels. Phloretin (0.25–1 mM) reduced Rb influx by ~60%, less affecting K loss. In Cl or NO3, 300 μM DIOA effectively inhibited K loss, but not Rb influx, a concentration tenfold higher than used to block K‐Cl cotransport. DCPIB (50 μM) mainly reduced K‐loss. Hence, hyposmotic K loss, through putative IK channels in hLECs, is associated with and/or rate‐limited by Cl loss through DIOA‐and phloretin‐sensitive anion channels whose nature awaits elucidation.