Figure 4. Caffeine evokes focal Ca²⁺ transients.

A, images of several smooth muscle cells loaded with the Ca²⁺ indicator Oregon-BAPTA. B-F show maps (drawn to the same scale and position as the image in A) of the location of focal Ca²⁺ transients occurring immediately after field stimuli (dots; B, D and F), or without stimuli (crosses; frames C, E and F), at some time over 20 min of recording in control (B, C and F) or in the presence of caffeine (3mM; D, E and F). Note that the evoked focal Ca²⁺ transients (NCTs) cluster in characteristic locations within parts of each cell (B). Caffeine induces spontaneous focal Ca²⁺ transients at additional locations (E; F, a composite of B and E).