Is intracellular pH a coupling factor in nutrient-stimulated pancreatic islets?

Area of Science:

• Endocrinology
• Cell Physiology
• Metabolic Research

Background:

• Intracellular pH (pHi) plays a crucial role in regulating cellular functions.
• Pancreatic islet cells are central to glucose homeostasis and insulin secretion.
• The precise role of pHi in nutrient-stimulated insulin secretion remains incompletely understood.

Purpose of the Study:

• To investigate the effects of pharmacological agents on intracellular pH (pHi) in rat pancreatic islet cells.
• To determine the impact of pHi modulation on nutrient- and non-nutrient-stimulated insulin secretion.
• To explore the relationship between pHi, calcium handling, and insulin secretion.

Main Methods:

• Monitoring of intracellular pH (pHi) using the fluorescent dye 2',7'-bis-carboxyethyl-5'(6')-carboxyfluorescein (BCECF).
• Treatment of dispersed rat pancreatic islet cells with weak acids (acetate, propionate, formate), amiloride, NH4Cl, and nutrients (glyceraldehyde, glucose, alpha-ketoisocaproate).
• Measurement of insulin secretion, inositol lipid metabolism, and fractional outflow rate of 45Ca2+.

Main Results:

• Weak acids and amiloride caused a rapid decrease in pHi, with amiloride preventing recovery.
• NH4Cl induced a pHi rise, while glucose and alpha-ketoisocaproate caused a sustained pHi increase; glyceraldehyde decreased pHi.
• NH4Cl inhibited nutrient-stimulated insulin secretion and inositol lipid metabolism, whereas amiloride potentiated glucose-induced responses and both reduced 45Ca2+ outflow.

Conclusions:

• Pharmacological modulation of pHi influences pancreatic islet cell functions, particularly calcium handling.
• Amiloride and weak acids reduce fractional 45Ca2+ outflow, suggesting a role in calcium regulation.
• Changes in pHi are unlikely to be the primary mechanism driving nutrient-stimulated insulin secretion.