Characterization of voltage-dependent Ca2+ channels in beta-cell line

Area of Science:

• Endocrinology
• Cell Biology
• Neuroscience

Background:

• Pharmacological studies suggest voltage-dependent calcium channels regulate insulin release.
• The existence of calcium channels insensitive to dihydropyridines and phenylalkylamines necessitates direct electrophysiological investigation.
• Understanding calcium channel involvement in pancreatic beta-cell function is crucial for stimulus-secretion coupling.

Purpose of the Study:

• To directly compare Ca2+ currents with insulin release in pancreatic beta cells.
• To investigate the role of voltage-dependent Ca2+ channels in stimulus-secretion coupling.
• To determine if dihydropyridine-sensitive Ca2+ channels mediate Ca2+ influx and insulin secretion.

Main Methods:

• Utilized the SV40-transformed pancreatic beta-cell line (HIT cells).
• Measured Ca2+ currents using the tight-seal whole-cell recording technique.
• Monitored cytosolic free-Ca2+ concentration ([Ca2+]i) with the fluorescent probe Fura 2.
• Stimulated insulin secretion by depolarizing cells with K+.

Main Results:

• Identified two components of Ca2+ current, both sensitive to the antagonist nimodipine.
• Demonstrated excellent agreement between nimodipine concentrations inhibiting Ca2+ currents, [Ca2+]i increase, and insulin release.
• Established an IC50 of 1.5 x 10(-9) M for nimodipine inhibition of insulin release.

Conclusions:

• The increase in [Ca2+]i in pancreatic beta cells upon depolarization is primarily mediated by dihydropyridine-sensitive Ca2+ channels.
• These findings provide direct evidence linking specific Ca2+ channels to insulin secretion.
• The study elucidates the mechanism of stimulus-secretion coupling in pancreatic beta cells.