Pancreatic beta (β)-cells secrete insulin in response to a rise in glucose and defective secretion contributes to type 2 diabetes. A rise in β-cell cytosolic Ca2+ triggers insulin exocytosis, and the endoplasmic reticulum (ER) and mitochondria both regulate cytosolic Ca2+ and secretion. Following ER Ca2+ release and reduced ER Ca2+, store-operated calcium entry (SOCE) serves to replete ER Ca2+. To understand the role of SOCE channels in β-cell function, we tested the actions of the SOCE channel blocker YM-58483 (YM) in isolated mouse islets and report that besides inhibiting SOCE activity, YM directly inhibited β-cell metabolism. The implications of these findings are discussed. Experimental Approach: Islets were isolated from mouse, cultured short term and studied using live cell imaging. The acute effects of YM on cytosolic, ER and mitochondrial Ca2+, cytoplasmic ATP/ADP, and KATP channels were monitored. In addition, the effects of YM on the oxygen consumption of isolated cardiac mitochondria were tested. Key Results: YM inhibited islet Ca2+ oscillations, suggesting a role for SOCE in the oscillations. However, YM also reduced ER and mitochondrial Ca2+ and lowered ATP/ADP. After preventing SOCE by removing extracellular calcium, YM still reduced ER, mitochondrial Ca2+ and ATP/ADP. Similar results were found using two other SOCE blockers. YM exposure increased single KATP channel openings, consistent a reduction of cytosolic ATP/ADP. Lastly, applying YM to isolated cardiac mitochondria increased leak flux and reduced ATP, demonstrating that YM directly inhibits mitochondrial OXPHOS.