Intracellular Ca2+ changes induced by in vitro ischemia in rat retinal slices

The effect of ischemia on intracellular Ca2+ concentration {[Ca2+](i)} in retinal slices was investigated. [Ca2+](i) in each layer of the retina was determined from fluorescence images in rat retinal slices loaded with fura2-AM. Ischemic like conditions were imposed on the retinal slice in vitro by perfusion with an oxygen/glucose deprived solution. All measurements were taken at 25 degreesC except when temperature dependence was examined. In response to 100 mm K+ or 0.2 ram glutamate under normoxic conditions, the [Ca2+], increase was higher in the inner retinal layers. Fifteen min ischemia evoked an increase in Ca2+ levels in all layers of the retina, and the rates of increase were especially high in the outer/inner segment layer and the outer nuclear layer. Ischemia in the absence of extracellular Ca2+ also induced a Ca2+ rise, but at lower rates than with standard ischemia. Intermittent ischemia, composed of three 15 min bursts of ischemia at 10 min intervals, promoted the Ca2+ rise. There was a more marked rise in [Ca2+](i) when the temperature was increased to 29 or 33 degreesC. Thus, in the rat retinal slice, in vitro ischemia evoked a more marked Ca2+ rise in the outer retina, which was in contrast to the Ca2+ responses to glutamate or high K+. The rates of increase in [Ca2+](i) with ischemia were larger rise. These increases appear at higher temperatures, and intermittent ischemia also promoted the Ca2+ to be derived from predominant influx of extracellular Ca2+ rather than release of intracellular Ca2+ stores. (C) 2001 Academic Press.