Do adipocytes contain high affinity sulfonylurea receptors

Area of Science:

• Endocrinology
• Cell Biology
• Pharmacology

Background:

• Sulfonylureas stimulate insulin secretion by interacting with receptors on pancreatic beta-cells.
• This interaction closes ATP-sensitive K+ channels, leading to cell depolarization and calcium influx.

Purpose of the Study:

• To investigate if sulfonylureas promote glucose uptake in 3T3-L1 cells and rat adipocytes via similar mechanisms.
• To determine the presence of high-affinity sulfonylurea receptors in adipose tissue.

Main Methods:

• Equilibrium binding and photoaffinity labeling with 125I-labeled 5-iodo-2-hydroxyglyburide.
• Assays for 86Rb+ efflux, intracellular calcium levels, and glucose uptake.
• Studies on hamster insulin-secreting tumor (HIT) cells for comparison.

Main Results:

• No high-affinity sulfonylurea receptor was detected on 3T3-L1 cells or rat adipocytes.
• Glyburide did not affect K+ channel activity, calcium levels, or glucose uptake in these cells.
• HIT cells showed expected glyburide effects, confirming assay validity.

Conclusions:

• Rat adipocytes and 3T3-L1 cells lack the high-affinity sulfonylurea receptor and do not respond to glyburide alone.
• The glucose-lowering effects of sulfonylureas are not mediated by direct enhancement of glucose uptake in adipose tissue.
• The primary site of action for sulfonylureas is the pancreatic beta-cell.