Acyl-Ghrelin Influences Pancreatic β-Cell Function by Interference with K_ATP Channels

Area of Science:

• Endocrinology and Metabolism
• Pancreatic Islet Biology
• Molecular Physiology

Background:

• Acyl-ghrelin (AG), a key hunger hormone, is also produced in the pancreas.
• Its precise role in pancreatic beta-cell function and insulin secretion remains incompletely understood.
• The involvement of ATP-sensitive K+ (KATP) channels in AG's action requires further elucidation.

Purpose of the Study:

• To investigate the direct effects of acyl-ghrelin (AG) on pancreatic beta-cell function.
• To determine the role of ATP-sensitive K+ (KATP) channels in mediating AG's actions.
• To identify the specific site of action for AG in the pancreatic beta-cell.

Main Methods:

• Electrophysiological recordings of KATP currents in beta-cells.
• Measurement of cytoplasmic calcium concentration ([Ca2+]c) and glucose-stimulated insulin secretion (GSIS).
• Experiments utilizing SUR1-knockout (KO) mice and specific receptor antagonists/agonists.

Main Results:

• AG hyperpolarized beta-cell membrane potential, decreased [Ca2+]c, and inhibited GSIS.
• These effects were abolished in SUR1-KO beta-cells, indicating a direct action on beta-cells.
• AG increased KATP current, suggesting indirect channel opening via the cAMP/protein kinase pathway.
• Unacylated ghrelin and GHSR1a antagonists/inverse agonists counteracted AG's effects.
• Inhibition of GSIS was prevented by cAMP modulators and a somatostatin receptor antagonist.

Conclusions:

• Acyl-ghrelin (AG) directly inhibits pancreatic beta-cell function and glucose-stimulated insulin secretion (GSIS).
• AG indirectly activates KATP channels, likely through interference with the cAMP pathway, leading to reduced insulin release.
• While AG acts directly on beta-cells, somatostatin receptors may play a modulatory role in its overall effect.