Quantitative evidence for merocrine secretion in insect midgut cells.
The occurrence of apical extrusions from cells has been observed on a large number of occasions in a wide variety of histological investigations. But whether the extrusions observed are a normal physiological event or are artefacts of the experimental procedures adopted has been the subject of much controversy. Lehane (1976a) described the extrusion of apical portions of the opaque zone midgut cells of Stomoxys calcitrans which contained large numbers of storage granules (merocrine secretion). This process involved the cell in the loss of cytoplasm, mitochondria and membranes as well as secretory products. If merocrine secretion is a normal physiological event rather than a fixation artefact then large falls should occur in the quantities of these components in the cell following the secretion burst. Using stereological methods the opaque zone cells were quantitatively described before and after the period in which merocrine secretion occurs (using these timings any possibility of producing apical extrusions as fixation artefacts was avoided). The results are entirely consistent with merocrine secretion having occurred. The volume of the cytoplasm falls by 23.74%, mitochondria by 30.55% and the total area of membrane in the cell by 32.59%.
Lehane
M J
MJ
School of Animal Biology, University of Wales, Gwynedd, UK.