Volume regulation of cultured, transformed, non-pigmented epithelial cells from human ciliary body

Electronic cell sizing has been used to measure the volume of cells suspended in isosmotic and in hyposmotic solutions of identical ionic composition. Without inhibitors, the cells displayed a regulatory volume decrease (RVD) following anisosmotic cell swelling with a time constant (tau) of 6.3 +/- 0.9 min (mean +/- S.E.). The RVD was markedly impaired by substituting gluconate for external Cl-, and tau was prolonged by: (i) reducing the chemical gradient favoring K+ loss (by elevating the external [K+] and blocking the Na. K-exchange pump), (ii) blocking the K+ channels with Ba2+, (iii) blocking Cl- channels and Cl-/HCO3 = exchange with DIDS, and (iv) removing external HCO3-. Withdrawing HCO3- may have altered the RVD either directly by inhibiting a Cl-/HCO3- antiport, or indirectly by affecting intracellular pH. The regulatory volume response of ODM Cl-2/SV40 cells is in several respects qualitatively similar to that of non-pigmented epithelial cells of the intact ciliary body. These common characteristics suggest that the cultured cells can serve as a useful model for studying solute and fluid transport across the human ciliary epithelium. The basis for the RVD is likely to be activation of separate K+ and Cl- channels, with or without the parallel operation of coupled K+/H+ and Cl-/HCO3- antiports.