This mouse study examined how pancreatic delta cell-derived somatostatin (SST) differentially inhibits alpha cells (via SSTR2) and beta cells (via SSTR3) to regulate glucagon and insulin secretion, using live fluorescent imaging of cAMP and Ca²⁺ sensors in intact and dissociated islets under postprandial-mimicking nutrient stimulation (high glucose + amino acids).
SSTR2 on alpha cells robustly suppresses both cAMP and Ca²⁺, while SSTR3 on beta cells suppresses cAMP but has significantly weaker potency over Ca²⁺. Blocking SSTR2 during nutrient stimulation raised local glucagon release, which in turn potentiated glucose-stimulated insulin secretion via beta cell GLP-1 receptors — revealing that delta cells tune insulin output by modulating intra-islet glucagon paracrine signaling.
- Findings are in mice only; receptor subtype distribution and signaling dynamics may differ in humans. - Ex vivo islet imaging may not fully recapitulate in vivo paracrine dynamics. - Constitutive fluorescent sensor expression could alter baseline cell physiology.
These findings reframe the delta cell not as a simple brake on both alpha and beta cells, but as a fine-tuner of insulin secretion amplitude through glucagon paracrine signaling. Clinically, SSTR2-selective targeting (e.g., with agonists or antagonists) could have distinct and opposite effects on insulin secretion compared with pan-SST strategies — a consideration for diabetes and islet therapeutics.
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