What are D (delta) cells?

Delta (D) Cells in the Pancreas

Delta cells are specialized endocrine cells in the pancreatic islets that secrete somatostatin, which acts as a paracrine inhibitor of insulin, glucagon, and somatostatin secretion, playing a crucial role in regulating glucose homeostasis. 1

Characteristics and Morphology

• Delta cells comprise approximately 5% of the cells in pancreatic islets but have complex morphology allowing them to establish extensive communication networks throughout the islet despite their scarcity 1, 2
• Delta cells are predominantly located in close proximity to capillaries (84%), with their immunoreactive material accumulated in cell parts facing the capillaries or perivascular spaces 3
• About 67% of delta cells tend to be arranged in contiguity to other delta cells, forming interconnected networks 3
• Delta cells have a distinctive morphology that allows them to interact with many more islet cells than their low numbers might suggest 1

Physiological Function

• Delta cells contain ATP-sensitive potassium channels (KATP channels) that close when glucose levels are elevated, initiating membrane depolarization and electrical activity that increases somatostatin secretion 1
• Somatostatin secreted by delta cells acts locally within the islets as a paracrine or autocrine inhibitor of insulin, glucagon, and somatostatin secretion 1, 2
• The inhibitory effects of somatostatin are mediated through activation of somatostatin receptors coupled to inhibitory G proteins, which suppress electrical activity and exocytosis in alpha and beta cells 1
• Factors released by neighboring alpha or beta cells can amplify glucose-induced effects on somatostatin secretion from delta cells, creating a feedback loop 1, 4

Cellular Connections and Communication

• Delta cells are electrically coupled to beta cells via gap junctions, suggesting they function as more than just paracrine inhibitors 2
• This gap junction communication between delta cells and beta cells creates a negative feedback loop that helps determine and stabilize the blood glucose set point 4
• Somatostatin released from delta cells reaches other islet cells mainly via the intrainsular circulation or along the perivascular space 3

Role in Disease States

• Somatostatin secretion is perturbed in animal models of diabetes mellitus, which may explain the loss of appropriate hypoglycemia-induced glucagon secretion 1
• This defect in glucagon secretion could potentially be mitigated by somatostatin receptor 2 antagonists 1
• The discovery of gap junction communication between delta cells and beta cells provides new insights into the contribution of delta cells to islet hormonal defects observed in both type 1 and type 2 diabetes 2
• Somatostatin antagonists or agents that suppress somatostatin secretion have been proposed as an adjunct to insulin therapy in diabetes treatment 1

Delta Cells in Other Tissues

• Delta cells are not exclusive to the pancreas; they have also been identified in the gastrointestinal tract, including the human colon and rectum 5
• In the digestive tract, these cells are fairly argyrophil (silver-staining) and correspond to somatostatin-immunoreactive cells 5
• The distribution and function of delta cells may vary between different tissues and organs 5

Human Translational Note: Understanding delta cell function has important clinical implications for diabetes management, as targeting somatostatin signaling could potentially improve glycemic control in patients with diabetes.

Human Translational Note: Understanding delta cell function has important clinical implications for diabetes management, as targeting somatostatin signaling could potentially improve glycemic control in patients with diabetes.