It is known that the density and distribution of mitochondria in a cell reflects its metabolic activity and function. At present, there is no general consensus on the preferential distribution of distinct subpopulations of mitochondria in pancreatic acinar cells (Tinel et al. 1999; Gonzalez et al. 2000). In this study the distribution of mitochondria in isolated pancreatic acinar cells and acinar cells of intact pancreas was investigated using confocal microscopy and transmission electron microscopy (TEM).

Pancreatic acinar cells were obtained from the isolated pancreas of CD-1 male mice killed by rapid cervical dislocation as described previously (Osipchuk et al. 1990). In isolated cells loaded with MitoTracker Red (fluorescent mitochondrial probe), mitochondria were predominantly situated in the peri-granular, subplasmalemmal and peri-nuclear regions. Subsequent applications of TEM fixatives caused partial leakage of the probe out of mitochondria, but overall the distribution of MitoTracker Red was unchanged, suggesting that the localization of mitochondria is not affected by the fixation procedure. TEM was performed on isolated acinar cells and on acinar cells of the intact pancreas. The distribution of mitochondria was quantified by calculating the percentage of cross-sectional area that mitochondria occupied in different regions: peri-granular, peri-nuclear and subplasmalemmal. In isolated acinar cells the highest density of mitochondria was in the peri-granular region, 25.69 ± 1.58 % (mean ± S.E.M.), then the subplasmalemmal region, 12.61 ± 0.77 %, and the peri-nuclear region, 9.07 ± 0.97 % (n = 26); each value was found to be significantly different (P < 0.01) from the non-specific and whole cell values using Student’s paired t test. Similar results were obtained from acinar cells of intact pancreas: peri-granular, 22.9 ± 1.95 %, subplasmalemmal, 12.45 ± 0.78 % and peri-nuclear regions, 9.05 ± 0.94 % (n = 26); these results were also significantly different from the non-specific and whole cell values (P < 0.01). Mitochondria were found only in cell areas where endoplasmic reticulum (ER) was present and a close localization between the ER membrane and the mitochondrial membrane could be seen.

We conclude that in pancreatic acinar cells mitochondria are preferentially distributed to peri-granular, subplasmalemmal and peri-nuclear regions in very close association with the ER and this distribution is not affected by isolation or fixation procedures.

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