OPTICAL MEASUREMENT OF STIMULUS-EVOKED MEMBRANE DYNAMICS IN SINGLE PANCREATIC ACINAR-CELLS

Stimulation of pancreatic acinar cells induces the release of digestiv e enzymes via the exocytotic fusion of zymogen granules and activates postfusion granule membrane retrieval and receptor cycling. In the pre sent study, changes in membrane surface area of rat single pancreatic acinar cells were monitored by cell membrane capacitance (C-m) measure ments and by the membrane fluorescent dye FM1-43. When measured with t he C-m method, agonist treatment evoked a graded, transient increase i n acinar cell surface area averaging 3.5%. In contrast, a 13% increase in surface area was estimated using FM1-43, corresponding to the fusi on of 48 zymogen granules at a rate of 0.5 s(-1). After removal of FM1 -43 from the surface-accessible membrane, a residual fluorescence sign al was shown by confocal microscopy to be localized in endosome-like s tructures and confined to the apical regions of acinar cells. The deve lopment of an optical method for monitoring the membrane turnover of s ingle acinar cells, in combination with measurements of C-m changes, r eveals coincidence of exocytotic and endocytotic activity in acinar ce lls after hormonal stimulation.