SWELLING ACTIVATES CHLORIDE CURRENT AND INCREASES INTERNAL CALCIUM IN NONPIGMENTED EPITHELIAL-CELLS FROM THE RABBIT CILIARY BODY

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 (similar to 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 (R(p)-cAMP-S) and cAMP mimic (S-p-cAMP-S). The data suggest independent involvement of Cl conductance and internal Ca in the regulation of cell volume in NPE cells. (C) 1995 Wiley-Liss, Inc.