ERG c-wave and pigment granule distribution in isolated chick retina: effects of osmotic pressure variation in vitreal perfusing solution.

The relation between osmotic gradient variation and change in the ERG c-wave was investigated. The vitreous side of the isolated chick retina was perfused with various solutions having osmotic pressures (pi v) ranging between 310 and 600 mOsm, while the choroidal side was maintained at 480 mOsm (pi c). When the osmotic difference (delta pi), (ie, pi v-pi c), was larger than -10 mOsm, normal c-waves with slow rise-times (cs-wave) were obtained; however, when the delta pi was smaller than -30 mOsm, c-waves with fast rise-times (cF-wave) were recorded. The peak time of the cS-waves ranged from 4-6 seconds, while that of the cF-waves was approximately 2 seconds. In addition, changes in the pigment granule distribution were also investigated histologically and photometrically. At delta pi of +10 mOsm, the distribution of pigment granules was similar to that in the dark-adapted chick retina. However, when the delta pi was -30 mOsm, the distribution of pigment granules was similar to that in the light-adapted chick retina. Under the control condition at delta pi of +10 mOsm, the pigment granules were distributed mainly within the cell body of the pigment epithelium, ie, in a direction opposite to the passive flow determined by the artificial osmotic gradient. However, after treatment by ouabain, the granules were spread toward the neural retina in the same direction as the passive flow, suggesting passive movement of these granules. These results suggest that a steep osmotic gradient is present within the normal retina and that the gradient is maintained by an ATPase-dependent mechanism. Moreover, the above results suggest that the cS-wave is scotopic and the cF-wave is photopic.