Cell-specific Ca(2+) responses in glucose-stimulated single and aggregated beta-cells

Area of Science:

• Endocrinology
• Cell Biology
• Biophysics

Background:

• Cytoplasmic calcium concentration ([Ca(2+)]) is vital for insulin exocytosis.
• Previous studies indicated a reproducible 'early [Ca(2+)]' response in individual ob/ob mouse beta-cells upon glucose stimulation.
• This suggests a cell-specific characteristic for beta-cell calcium signaling.

Purpose of the Study:

• To determine if the cell-specific cytoplasmic calcium response is a general phenomenon in rodent beta-cells.
• To investigate if this cell-specific response is observable in functionally coupled beta-cells.
• To identify reliable markers for this cell-specific response.

Main Methods:

• Utilized the fura-2 technique to measure cytoplasmic calcium concentration.
• Studied single dispersed beta-cells, beta-cell clusters of varying sizes, and intact islets from ob/ob and lean mice, as well as rat beta-cells.
• Applied repeated glucose stimulation (20mM) and analyzed parameters like lag-time, nadir of initial lowering, and peak height.

Main Results:

• Significant correlations were found between consecutive glucose stimulations for lag-time, nadir, and peak height in single dispersed beta-cells and beta-cells within clusters of all sizes.
• These correlations were also observed in single dispersed beta-cells from lean mice and rats.
• Lag-time and peak height correlations persisted even in intact ob/ob mouse islets.

Conclusions:

• Despite heterogeneity among individual beta-cells, the 'early [Ca(2+)]' response exhibits cell-specific characteristics.
• Lag-time for calcium rise, nadir of initial lowering, and first peak height serve as identifiable cell-specific markers.
• These findings confirm a general phenomenon of cell-specific calcium responses in rodent beta-cells, relevant for insulin secretion.