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The Relationship between Membrane Potential and Calcium Dynamics in Glucose-Stimulated Beta Cell Syncytium in Acute Mouse Pancreas Tissue Slices

Figure 6

Simultaneous recording of [Ca2+]i and membrane potential oscillations during stimulation with 12 mM glucose.

A VF (left panel) stained mostly cell membranes while Rhod-2 (middle panel) stained cell cytoplasms, without any significant co-localization of the two dyes in the active regions (right panel; see also Figure S4). B A color-coded representation of selected responsive cells with respect to the time lag between the oscillation start50 of the first cell and every other cell for the VF signal (left panel), Rhod-2 signal (middle panel) and merge of the two (right panel). The outline stands for the VF signal and the interior for Rhod-2. Both membrane potential and [Ca2+]i wave roughly spread from top to bottom of the focal plane. Note that in any given cell, the membrane signal precedes (colder color) the [Ca2+]i signal, indicating that depolarization precedes the increase in [Ca2+]i. C Time traces of the VF and Rhod-2 signals from three cells indicated in the right panel of B show a wave-like spreading of both signals. In all cells, the VF signal clearly preceded the Rhod-2 signal. Arrows indicate the widths of oscillations at their half-maximal amplitude (see Methods). Y axis represents the normalized fraction of the difference between maximum and plateau baseline fluorescence. D Average trajectory for [Ca2+]i oscillation starts50 (solid line) and ends50 (dashed line). E Average trajectory for the membrane potential oscillation starts50 (solid line) and ends50 (dashed line). In D and E, numbers indicate angles in degrees. F Time lag between ends50 (1st quartile=284 ms, median= 360 ms, 3rd quartile=473 ms) was significantly larger than the time lag between starts50 (1st quartile=133 ms, median=170 ms, 3rd quartile=189 ms, n=21 cells) of the Rhod-2 and VF signals. Asterisks indicate p<0.001 (Mann-Whitney test). Resolution was 256x128 pixels at 52 Hz.

Figure 6