The beta-cell glibenclamide receptor is an ADP-binding protein

Area of Science:

• Cell Biology
• Endocrinology
• Pharmacology

Background:

• ATP-sensitive potassium channels (K-ATP channels) play a crucial role in regulating insulin secretion from pancreatic beta-cells.
• Sulfonylureas are known to inhibit K-ATP channels and stimulate insulin release, but the role of other nucleotides is less understood.

Purpose of the Study:

• To investigate the effects of adenosine diphosphate (ADP) on K-ATP channel activity, calcium concentration, and insulin secretion in a hamster pancreatic beta-cell line (HIT T15).
• To determine if ADP shares binding sites with sulfonylureas on beta-cell membranes.

Main Methods:

• Studied [3H]glibenclamide binding to membranes and whole cells.
• Assayed K-ATP channel activity by measuring 86Rb efflux.
• Measured intracellular Ca2+ concentration using the fluorescent dye quin 2.
• Quantified insulin release from HIT cells.

Main Results:

• ADP competitively inhibited [3H]glibenclamide binding in a dose-dependent manner.
• ADP inhibited K-ATP channel activity, reducing 86Rb efflux.
• ADP increased intracellular Ca2+ concentration and stimulated insulin release, particularly in the presence of extracellular calcium and glucose.
• These effects were specific to ADP and not observed with other nucleotides.

Conclusions:

• ADP and sulfonylureas likely share common binding sites on the extracellular side of beta-cell plasma membranes.
• ADP's inhibition of K-ATP channels leads to increased intracellular Ca2+ and subsequent insulin secretion.
• ADP represents a novel signaling molecule involved in the regulation of pancreatic beta-cell function.