Figure 6. Glucose-stimulated cAMP does not require Ca²⁺ elevation.

A. Islets expressing cAMP reporter were loaded with Fura-2 to measure Ca²⁺ and cAMP concurrently. In response to glucose (11G, grey bar), the increase in cAMP (black trace) precedes Ca²⁺ elevation and oscillations (blue trace). B–D. Glucose-stimulated cAMP in β-cells is independent of [Ca²⁺]_i. B. Glucose–evoked Ca²⁺ oscillations are completely eliminated in the absence of extracellular Ca²⁺, as widely reported for β-cells. Trace shows Fura 2 responses (F340/F380) to 11 mM glucose (grey bars, 11G) before, during and after the depletion of extracellular Ca²⁺. C. In contrast, glucose-evoked cAMP responses persist when extracellular Ca²⁺ is removed. D. Mean responses from Ca²⁺ - and cAMP imaging to 11 mM glucose before, during, and after Ca²⁺ is removed from bath (±s.e.m., n = 6 islets each). Ca²⁺- and cAMP-imaging were conducted independently to prevent any spectral overlap.