INWARD PERMEABILITY OF LITHIUM AND RUBIDIUM FOLLOWING LIGHT EXPOSURE TO THE RAT RETINA MEASURED BY SIMS

Retinal light damage is a complex process mediated by many interrelate d factors. We hypothesized that excessive light exposure in rats would alter the electrolyte levels in the retina so that ionic homeostasis could not be maintained, and both photoreceptor and retinal pigment ep ithelial cells would degenerate.Pigmented Long-Evans rats were exposed to 110-210-foot candles of white fluorescent light for 5 minutes of e very hour, then returned to room light (50 foot-candles). The total cu mulative exposure was 20, 40, or 60 minutes. Animals were sacrificed i mmediately after the last light exposure or after 7 days in cyclic roo m light. Just prior to sacrifice, animals were given an intravenous bo lus of Ringer's solution which circulated for 5 minutes. In order to d etect entry of exogenous ions into the retina, half the animals were g iven Ringer's solution in which Li and Rb were substituted for Na and K. Measurement of elements in freeze-dried retinal sections was analyz ed by digitized ion images generated by secondary ion mass spectrometr y (SIMS). The results showed no difference in electrolyte levels (Na, K, Li, or Rb) between control retinas and retinas that had been expose d to light, but had normal retinal morphology. There was increased inw ard permeability of Li and Rb from the choroidal circulation only when there was focal loss of the retinal pigment epithelium (RPE) in a pho totoxic lesion. Lithium did not enter the retina from the retinal vasc ulature. Rubidium is normally present in the ocular tissues. SIMS is u seful for detection and localization of lithium and rubidium in biolog ical samples.