Calcium affects insulin release and membrane potential in islet beta-cells

Area of Science:

• Endocrinology
• Cell Physiology
• Pancreatic Beta-Cell Function

Background:

• Insulin secretion is a complex process regulated by various ions and cellular electrical activity.
• The roles of calcium (Ca) and magnesium (Mg) in glucose-stimulated insulin release (GSIR) and their interplay with membrane potential require further elucidation.

Purpose of the Study:

• To investigate the relationship between insulin release and beta-cell membrane potential under varying Ca and Mg concentrations.
• To determine how alterations in Ca and Mg levels affect GSIR and cellular electrical activity.

Main Methods:

• Perfusion of rat pancreas and perifusion of mouse islets to measure insulin release.
• Electrophysiological recordings of single beta-cell membrane potentials.
• Manipulation of extracellular Ca and Mg concentrations during glucose stimulation.

Main Results:

• Beta-cell depolarization correlated with insulin release, while hyperpolarization suppressed it, independent of Ca concentration.
• Reduced Ca and Mg maintained GSIR with sustained depolarization and altered burst activity patterns.
• Re-addition of Ca and Mg transiently suppressed insulin release, linked to hyperpolarization, primarily due to Ca.

Conclusions:

• Relative Ca and Mg concentrations and membrane potential are critical determinants of insulin release.
• Under specific conditions, Ca can inhibit GSIR, potentially by enhancing potassium permeability.