Ryanodine receptors are involved in nuclear calcium oscillation in primary pancreatic β-cells

Ryanodine receptors (RyRs) are mainly located on the endoplasmic reticulum (ER) and play an important role in regulating glucose-induced cytosolic Ca ²⁺ oscillation in pancreatic β-cells. However, subcellular locations and functions of RyRs on other cell organelles such as nuclear envelope are not well understood. In order to investigate the role of RyRs in nuclear Ca ²⁺ oscillation we designed and conducted experiments in intact primary pancreatic β-cells.Immunocytochemistry was used to examine the expression of RYRs on the nuclear envelope. Confocal microscopy was used to evaluate the function of RYRs on the nuclear envelope. We found that RyRs are expressed on the nuclear envelope in single primary pancreatic β-cells and isolated nuclei. Laser scanning confocal microscopy studies indicated that application of glucose to the cells co-incubated with Ca ²⁺ indicator Fluo-4 AM and cell-permeable nuclear indicator Hoechst 33342 resulted in nuclear Ca ²⁺ oscillation. The pattern of glucose-induced Ca ²⁺ oscillation in the nucleus and cytosol was similar. The reduction of Ca ²⁺ oscillation amplitude by ryanodine was much greater in the nucleus though both the cytosol and the nucleus Ca ²⁺ amplitude decreased by ryanodine.Our results suggest that functional ryanodine receptors not only exist in endoplasmic reticulum but are also expressed in nuclear envelope of pancreatic β-cells.