Fig. 8

Schematic summarising the effects of insulin in δ cells. Relationship between SGLT2-mediated glucose uptake and δ-cell electrical activity, Ca²⁺ entry, Ca²⁺-induced Ca²⁺ release (CICR) and somatostatin release. Insulin stimulates SGLT2 activity. The operation of SGLT2 is electrogenic Na⁺-dependent glucose uptake mediated by SGLT2 gives rise to a small depolarising current and may (in some cells with sufficiently high SGLT2 expression and/or low K_ATP channel activity) trigger electrical activity (action potential firing). The associated increase in cytoplasmic Ca²⁺ ([Ca²⁺]_i) leads to intracellular Ca²⁺ mobilisation by activation of ryanodine receptors (RyRs) and Ca²⁺-induced Ca²⁺ release (CICR). In addition to SGLT2, the δ cells also express the glucose transporters GLUT1 and GLUT3. Glucose uptake via these transporters accounts for 99% of glucose uptake. Metabolism of glucose leads to K_ATP channel closure, membrane depolarisation, electrical activity and CICR