Swelling activates chloride current and increases internal calcium in nonpigmented epithelial cells from the rabbit...

Membrane current and [Ca]i in rabbit nonpigmented ciliary body epithelial cells (NPE cells) were monitored with combined patch-clamp and fura-2 measurements during cell swelling induced by anisosmotic conditions. In the presence of K-channel blockers, cell swelling produced an increase in membrane current, accompanied by an increase in [Ca]i. Structural changes in the cell, associated with membrane deformation, may be the cause of the increase in [Ca]i during swelling. The conductance activated by swelling was permeable to Cl: it was dependent on the Cl concentration gradient across the cell membrane, and it was blocked by the Cl-channel blockers DIDS, SITS, NPPB, and DIOA. Although swelling increased both Cl current and [Ca]i, there was no evidence that Ca was involved in the regulation of the Cl conductance. Cell swelling activated the current even when [Ca]i was strongly buffered at an elevated level (500 nM) or at a low level (approximately 0) with internal Ca-BAPTA/Cs-BAPTA mixtures. In addition, Cl conductance was unaffected when [Ca]i was increased with a Ca ionophore. There was also no evidence that cAMP participates in the regulation of the Cl conductance: swelling activation of the current occurred in the presence of cAMP inhibitor (Rp-cAMP-S) and cAMP mimic (Sp-cAMP-S). The data suggest independent involvement of Cl conductance and internal Ca in the regulation of cell volume in NPE cells.