PKC-SENSITIVE CL- CHANNELS ASSOCIATED WITH CILIARY EPITHELIAL HOMOLOG OF PI(CLN)

Swelling activates and protein kinase C (PKC) downregulates Cl- channels in cultured nonpigmented ciliary epithelial (NPE) cells. We now report that the PKC inhibitor staurosporine upregulates whole cell. Cl- currents isosmotically. The kinetics and current-voltage relationship are similar to those of volume-activated Cl- channels of these cells. These properties are inconsistent with cloned ClC-0, ClC-1, ClC-2, and MDR1 channels but could reflect the cystic fibrosis transmembrane conductance regulator (CFTR) channel or the Cl- channel regulator pI(Cln). CFTR mRNA was undetectable by Northern analysis of cultured NPE cells or ciliary body tissue. In contrast, a human pI(Cln) probe obtained by polymerase chain reaction cloning and showing 90% identity with the rat cDNA clone detected high levels of transcripts in NPE cells. The level was low in tissue, where the NPE message was diluted by RNA from other cells. We conclude that NPE cells display staurosporine-activated Cl- channels [g(St)(Cl)] likely identical with the volume-activated channels. The same cells expressing gst(Cl) transcribe mRNA for a novel homologue (pHCBI(Cln)) of pI(Cln) that may regulate Cl- transport into the aqueous humor.