Calcium signaling in Müller cells is necessary to evoke capillary but not arteriole dilation. A, The diameter of intermediate layer capillaries was monitored. GCL, Ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; OPL, outer plexiform layer. B, C, In eyecups, mean responses from intermediate layer capillaries show that stimulation evoked dilations in control mice (Ctrl) but not in IP3R2−/− littermates (n = 13 vessels from 4 control eyecups, n = 15 vessels from 4 IP3R2−/− eyecups; unpaired t test, p = 0.015; control, 7.6 ± 3.0% vessel dilation; IP3R2−/−, −0.37 ± 1.1% vessel dilation). D, The diameter of arterioles was monitored. E, F, Stimulation also evoked arteriole dilation in control mice. This dilation was not diminished in IP3R2−/− littermates (n = 6 vessels from 3 control eyecups, n = 7 vessels from 3 IP3R2−/− eyecups; unpaired t test, p = 0.72; control, 6.0 ± 1.2% vessel dilation; IP3R2−/−, 6.7 ± 1.2% vessel dilation). G, H, Similar responses were observed in vivo. Mean responses from intermediate layer capillaries show stimulus-evoked dilations in control mice but not in IP3R2−/− littermates (n = 14 vessels from 5 control mice, n = 14 vessels from 5 IP3R2−/− mice; unpaired t test, p = 0.0092; control, 1.1 ± 0.39% vessel dilation; IP3R2−/−, −0.25 ± 0.29% vessel dilation). I, J, Stimulus-evoked arteriole dilation in arterioles of control mice was not diminished in IP3R2−/− littermates (n = 5 vessels from 5 control mice, n = 5 vessels from 5 IP3R2−/− mice; unpaired t test, p = 0.41; control, 6.2 ± 1.9% vessel dilation; IP3R2−/−, 8.1 ± 1.0% vessel dilation). *p < 0.05; **p < 0.01.