Glucose and NAADP trigger elementary intracellular β-cell Ca²⁺ signals

Area of Science:

• Cellular Biology
• Endocrinology
• Biochemistry

Background:

• Pancreatic beta cells regulate blood glucose by releasing insulin.
• Current models focus on ATP-sensitive potassium (KATP) channels for glucose-stimulated insulin secretion.
• The KATP channel pathway may not fully explain all beta cell responses to glucose.

Purpose of the Study:

• To investigate the role of NAADP-evoked calcium release in pancreatic beta cell stimulus-secretion coupling.
• To demonstrate the existence and characteristics of elementary intracellular calcium signals mediated by NAADP.
• To propose a novel mechanism for glucose-induced insulin secretion involving localized calcium signaling.

Main Methods:

• Total internal reflection fluorescence (TIRF) microscopy to visualize elementary calcium signals.
• Application of glucose and NAADP to pancreatic beta cells.
• Optical quantal analysis to characterize calcium event amplitudes.

Main Results:

• Glucose and NAADP induce highly localized elementary intracellular calcium signals in beta cells.
• These signals were previously obscured by global calcium measurements and SERCA activity.
• Optical quantal analysis confirmed the unitary amplitude of NAADP-evoked calcium events, comparable to IP3 receptor blips and ryanodine receptor quarks.

Conclusions:

• NAADP-evoked localized calcium release is a key component of stimulus-secretion coupling in pancreatic beta cells.
• This mechanism provides a novel explanation for initial beta cell responses to elevated blood glucose.
• Understanding these elementary calcium signals may offer new insights into type 2 diabetes pathophysiology.