Figure 1: Characteristics and prevalence of spontaneous calcium transients.

A) A diagrammatic representation of stimulated MET channel activity. When the hair bundle deflects (black arrow) there is an increased tension in the tip link (green). This increases the open probability of the MET channel and results in an influx of cations. B) A top-down view of a hair bundle with calcium transients in individual stereocilia, indicated by an increased GCaMP3 signal. Scale bar is 2 μm. C) Temporal color-coded projections of spontaneous calcium transients are shown in a P7 inner hair cell (left), P4 outer hair cell (middle) and P6 vestibular hair cell (right). The transients do not appear to be spatially or temporally correlated. Scale bar is 2 μm. D) The stereocilium marked by a blue rectangle is plotted over time, with a time interval of 500 ms. An individual calcium transient in this stereocilium is shown on the right panel. GCaMP3 signal increases sharply within a span of 500 ms and decays gradually over 3 s. The same stereocilium tip displays variable but step-like changes in intensity over a longer time period. The steps are marked by red dotted lines. Scale bar is 1 μm. E) Montage of a calcium transient over time in a P6 inner hair cell with GCaMP3. Red arrowhead points to the stereocilium displaying the activity. Each frame is 1.2 s apart. Scale bar is 2 μm.