Heterogeneity in Cytosolic Calcium Regulation among Different Microvascular Smooth Muscle Cells of the Rat Retina

Rat retinae were dissociated to yield intact microvessels 7 to 42 μm in diameter. These were loaded with fura-2 AM and single fragments anchored down in a recording bath. Intracellular Ca2+ levels from 20- to 30-μm sections of vessel were estimated by microfluorimetry. The vessels studied were identified as metarterioles and arterioles. Only the microvascular smooth muscle cells loaded with fura-2 AM and changes in the fluorescence signal were confined to these cells: Endothelial cells did not make any contribution to the fluorescence signal nor did they contribute to the actions of the drugs. Caffeine (10 mM) or elevated K+ (100 mM) produced a transient rise in cell Ca2+ in the larger vessels (diameters >18 μm) but had no effect on smaller vessels (diameters 30 min) on washing out the endothelin and the vessel failed to relax. These results demonstrate heterogeneity between smaller and larger retinal vessels with regard to Ca2+ mobilisation and homogeneity with respect to the actions of vasoactive peptides.