Related Experiment Videos
Temperature-sensitive random insulin granule diffusion is a prerequisite for recruiting granules for release
Rosita Ivarsson1, Stefanie Obermüller, Guy A Rutter
1The Diabetes Programme at Lund University, Department of Physiological Sciences, BMC B11, SE-221 84 Lund, Sweden.
Traffic (Copenhagen, Denmark)
|September 10, 2004
Summary
Cooling suppresses insulin granule movement by affecting frequency more than velocity, indicating random diffusion is key for directed transport and second-phase insulin secretion.
Area of Science:
- Cell Biology
- Endocrinology
- Biophysics
Background:
- Glucose stimulates insulin secretion via a biphasic process involving intracellular granule movement.
- Understanding the dynamics of insulin granule transport is crucial for explaining secretion patterns.
Purpose of the Study:
- To investigate the relationship between random and directed insulin granule movement and exocytotic capacity.
- To determine the impact of temperature on these movement modes and their contribution to insulin secretion.
Main Methods:
- Live confocal imaging of EGFP-labeled insulin granules in INS-1 cells.
- Capacitance measurements to assess exocytosis.
- Temperature reduction experiments (34°C to 24°C).
Main Results:
- Cooling significantly reduced the frequency (81%) but minimally affected the velocity (25%) of directed insulin granule movements.
- Temperature sensitivity was much higher for the frequency of directed events (Ea ≈ 135 kJ/mol) than for velocities (Ea ≈ 22 kJ/mol).
- Cooling suppressed random granule diffusion by ~50%; directed event frequency correlated with diffusion extent.
- Only the second phase of biphasic insulin secretion was affected by cooling.
Conclusions:
- Random granule diffusion is essential for directed transport and the mobilization of granules during the second phase of insulin secretion.
- The temperature sensitivity suggests that factors other than motor protein ATPase activity regulate directed insulin granule movement frequency.