The sequestration of [Ca2+]i in the cisternae of ER accompanying the cortical or peripheral actin in the Sertoli cells could induce modifications in affinity of the Ca2+-dependent actin-interacting protein scin-derin for either the cytosol, the phospholipids of the membrane, or actin; these modifications, in turn, could prove significant in the physiology of the Sertoli cell junctions that are responsible for the maintenance of the blood-testis barrier or for the release of mature spermatids. In Ma-din-Darby canine kidney (MDCK) confluent cell cultures, tight junctions failed to develop when extracellular Ca2+ levels were low.
Elevation of [Ca2+]i concentration during cell injury has been reported to close gap junctions, suggesting that both tight and gap junctions are responsive to [Ca2+]i levels. Ca2+-containing precipitates were localized in the cisternae of ER associated with the Sertoli cell junctions at the electron microscope level by ion-capture cytochemistry using combined oxalate and py-roantimonate methods. In smooth- and non-muscle tissues, the Ca2+ storage compartment is believed to be associated with the ER. The appearance of scinderin-positive deposits in the cytoplasm of Sertoli cells during stages of the cycle that precede the release of mature spermatids may reflect transient changes in the availability of [Ca2+]i stored in the cisternae of ER.