ACTIVATION OF CL- CURRENTS IN CULTURED RAT RETINAL-PIGMENT EPITHELIAL-CELLS BY INTRACELLULAR APPLICATIONS OF INOSITOL-1,4,5-TRIPHOSPHATE - DIFFERENCES BETWEEN RATS WITH RETINAL DYSTROPHY (RCS) AND NORMAL RATS

Using the whole-cell configuration of the patch-clamp technique, we st udied the conditions necessary for the activation of Cl--currents in r etinal pigment epithelial (RPE) cells from rats with retinal dystrophy (RCS) and nondystrophic control rats. In RPE cells from both rat stra ins, intracellular application of 10 mu M inositol-1,4,5-triphosphate (IP3) via the patch pipette led to a sustained activation of voltage-d ependent Cl- currents, blockable by 1 mM 4,4'-diisothiocyanatostilbene -2,2'-disulfonic acid (DIDS). IP3 activated Cl- currents in the presen ce of a high concentration of the calcium chelator BAPTA (10 mM) in th e pipette solution, but failed to do so when extracellular calcium was removed. Intracellular application of 10(-5)M Ca2+ via the patch pipe tte also led to a transient activation of Cl- currents. When the cells were preincubated in a bath solution containing thapsigargin (1 mu M) for 5 min before breaking into the whole-cell configuration, IP3 fail ed to activate voltage-dependent currents. Thus, IP3 led to release of Ca2+ from cytosolic calcium stores. This in turn activated an influx of extracellular calcium into the submembranal space by a mechanism as yet unknown, leading to an activation of calcium-dependent chloride c urrents. In RPE cells from RCS rats, which show an increased membrane conductance for calcium compared to normal rats, we observed an accele rated speed of Cl--current activation induced by IP3 which could be re duced by nifedipine (1 mu M). Thus, the increased membrane conductance to calcium in RPE cells from RCS rats changes the response of the cel l to the second messenger IP3.