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Fig. 4. Time course of peptide release and luminal pH changes. (A,B) Cells expressing VAMP-pHluorin or IAPP-emerald (IAPP-EMD) were voltage-clamped and their footprint imaged at 10 Hz. Example images taken in separate cells transfected with IAPP-EMD (A) or VAMP-pHluorin (B) at the indicated times relative to the onset of a 500 millisecond depolarization from -70 mV to zero mV. (C) Time course of IAPP-EMD fluorescence (lower trace) in the ROI indicated by the circle in A in response to a 500 millisecond depolarization (top trace). Note that the IAPP-EMD fluorescence disappears after a delay of 
2 seconds. (D) As in C for the experiment shown in B. Note that the VAMP-pHluorin trace rises abruptly to a plateau from which it declines mono-exponentially after a delay of 1 second. The gray line superimposed on the data points represents the best fit of a discontinuous function consisting of a straight-line segment followed by a mono-exponential decay to the remainder of the trace, using the first point of the rising phase as the start of the event. (E) Cumulative histograms showing the time, relative to stimulation, of the loss of IAPP-EMD fluorescence (squares), the increase in VAMP-pHluorin fluorescence (circles) analyzed as indicated by arrows in C and D. The functions superimposed on histograms in E are exponential functions fitted to the distributions yielding 
-values of 0.9±0.1 (circles), and 2.2±0.2 seconds (squares). For comparison, the function from Fig. 3B (fit to the nucleotide release data >500 milliseconds) is included as a dotted line.
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