L-type VGCCs regulate the circadian control of retinoschisin secretion and content. The culture media and retinal tissue from whole retina cultures were harvested at CT 5 (subjective day) and CT 17 (subjective night) for immunoblotting assays. (a) Immunoblots show the secreted retinoschisin in the media, protein content of retinoschisin in the whole retina, and loading control (whole retina total Erk). Treatment with an L-type VGCC blocker, nitrendipine (3 μM), for 2 hours decreased the secreted retinoschisin and the protein content of retinoschisin in the whole retina during the subjective night (CT 17) but not subjective day (CT 5). (b) Secretion of retinoschisin was under circadian control, which was significantly higher during the subjective night (CT 17) than during the subjective day (CT 5). Nitrendipine treatment abolished the circadian rhythms of secreted retinoschisin in the media. (c) Similar results were observed in retinoschisin protein expression in cultured whole retinas. n = 3 or 4 in each group. Comparisons were made between CT 5 and CT 17 using Student’s t-test (*P < 0.05).