Quantitative evidence for merocrine secretion in insect midgut cells

Area of Science:

• Cell Biology
• Insect Physiology
• Histology

Background:

• Apical extrusions in cells are frequently observed but their physiological nature is debated.
• Lehane (1976a) described merocrine secretion in Stomoxys calcitrans midgut cells, involving loss of cytoplasm, mitochondria, membranes, and secretory products.
• Distinguishing physiological merocrine secretion from fixation artifacts is crucial.

Purpose of the Study:

• To quantitatively determine if merocrine secretion in Stomoxys calcitrans midgut cells is a normal physiological event.
• To assess the impact of merocrine secretion on cellular components, differentiating it from experimental artifacts.

Main Methods:

• Stereological methods were employed for quantitative description of cells.
• Opaque zone midgut cells of Stomoxys calcitrans were analyzed before and after the merocrine secretion period.
• Cellular components, including cytoplasm, mitochondria, and membrane area, were measured.

Main Results:

• Quantitative analysis demonstrated significant reductions in cellular components consistent with merocrine secretion.
• Cytoplasm volume decreased by 23.74%.
• Mitochondria volume decreased by 30.55%, and total membrane area decreased by 32.59%.

Conclusions:

• The observed quantitative changes strongly support merocrine secretion as a normal physiological process in these cells.
• The findings refute the hypothesis that apical extrusions are solely fixation artifacts.
• Merocrine secretion involves a substantial loss of cellular material, including cytoplasm, mitochondria, and membranes.