Insulin secretion and IP levels in two distant lineages of the genus Mus: comparisons with rat islets

Islet responses of two different Mus geni, the laboratory mouse (Mus muscul us) and a phylogenetically more ancient species (Mus caroli), were measured and compared with the responses of islets from rats (Rattus norvegicus). A minimal and flat second-phase response to 20 mM glucose was evoked from M. musculus islets. whereas a large rising second-phase response characterize d rat islets. M. caroli responses were intermediate between these two extre mes; a modest rising second-phase response to 20 mM glucose was observed. P rior, brief stimulation of rat islets with 20 mM glucose results in an ampl ified insulin secretory response to a subsequent 20 mM glucose challenge. N o such potentiation or priming was observed from M. musculus islets. In con trast, M, caroli islets displayed a modest twofold potentiated first-phase response upon subsequent restimulation with 20 mM glucose. Inositol phospha te (IP) accumulation in response to 20 mM glucose stimulation in [H-3] inos itol-prelabeled rat or mouse islets paralleled the insulin secretory respon ses. The divergence in 20 mM glucose-induced insulin release between these species may be attributable to differences in phospholipase C-mediated IP a ccumulation in islets.