Alterations in glucose tolerance and tendency toward impaired insulin secretion, which were apparent in vivo, may reflect altered signal generation by glucose. We next used the fluorescent intracellular probe Fluo 2 (27) to monitor intracellular free Ca2+ dynamics in β-cells in situ within the intact islet (Figs. 10 and 11). Under the conditions used, glucose-induced changes in free Ca2+ were largely restricted to the β-cell population (10, 27). No genotype-dependent differences in the peaks of the Ca2+ response to either high glucose or KCl were apparent in islets from male mice (Fig. 10), although islets from male βVps13cKO mice fed RC did display a significantly delayed response to high glucose stimulation (Fig. 10A, ii and v). Increases in free Ca2+ in islets from female mice were respectively augmented (Fig. 11A, i and vi) and reduced (Fig. 11B, i and vi) in high-glucose-stimulated islets from βVps13cKO animals fed RC or HFD. A similar trend was seen after depolarization with KCl (Figs. 11A, i and viii, and B, i, iv, and viii). As was the case for male mice, the response to glucose in islets from HFD-fed female mice was slightly delayed, with those from RC mice showing no significant difference in the time of the glucose peak (Fig. 11A, i and v, and B, i and v).