A longitudinal study of parotid secretory kinematics by cinemicrography and computer analysis

The kinematic responses of parotid gland acini to isoproterenol were studied in vitro by time-lapse cinemicrography. It was shown that once secretion begins, granule depletion accelerates to a maximum rate in 8-10 min, continues at a steady rate for 5-8 min and then slows, depletion becoming essentially complete 25-30 min after stimulation. The continuum of morphologic change manifested by the acinar lumen during secretion was quantified by computer analysis of sequential cine-frames representing a time resolution of 0.1 min. Interpretation of seventh-order and eleventh-order polynominal non-linear least squares trend curves shows that the lumen enlarges from an initial cross-sectional area of approximately 96 mum2 at 14.9 min. The shape of these curves suggests that after an initial partial enlargement the lumen shrinks (or remains steady) before climbing to the maximum. The basic pattern resembles distortion curves characteristic of two-phase viscoelastic compliance systems. It is also shown that luminal plasma membranes undergo a very active ebb and flow during the egestive phase of secretion.