Fig. 10.
“Depressed” capacitance responses are not an artifact of simultaneous endocytosis. A, Top trace(Cm): Capacitance trace from a cell stimulated with 40 msec duration pulses at 200 msec intervals (20 pulses). Timing of depolarizations is indicated by gapsin the trace and by the vertical bars below.Middle traces (Iamp): Amperometric recording during the same stimulus shown on an expanded (above) and compressed (below) time scale. Timing of depolarizations is indicated below each trace.Bottom, Left axis: Plot of cumulativeCm increases against cumulative Ca2+ entry. The dashed curve is a plot of the standard transfer function. The Ca2+-exocytosis relationship of this cell is strongly depressed. Right axis: The amperometric signal during the stimulus train was integrated and is expressed in picocoulombs. For comparison to the capacitance response, the maximum amperometric response was aligned with the maximumCm increase and plotted against cumulative Ca2+ entry (solid line).B, The same cell was stimulated with 40 msec duration pulses at 1000 msec intervals (15 pulses). Calculation of ΔCm was performed by using only the first 200 msec after each depolarization. Calculation ofQamp was performed by integrating the current during and for 200 msec after each depolarization. All traces, plots, and vertical scales as in A. Cell L080104.