Small Mouse Islets Are Deficient in Glucagon-Producing Alpha Cells but Rich in Somatostatin-Secreting Delta Cells

Small and big mouse islets were compared with special reference to their content of glucagon-producingα-cells and somatostatin-producingδ-cells. Areas stained for glucagon and somatostatin were measured in the largest cross section of small (diameter < 60 μm) and big (diameter > 100 μm) islets. Comparison of the areas indicated proportionally moreδ- thanα-cells in the small islets. After isolation with collagenase these islets were practically devoid ofα-cells. We evaluated the functional importance of the islet size by measuring the Ca2+signal for insulin release. A majority of the small islets responded to the hyperpolarization action of somatostatin with periodic decrease of cytoplasmic Ca2+when glucose was elevated after tolbutamide blockade of theKATPchannels.