FIGURE 3.

Visualization of the picoliter volume of a microchamber holding a single ventricular myocyte. The extracellular dye (Ca²⁺ bound Fluo-3) was excited with a two-photon laser and series of optical sections along the z-axis were recorded. (A) Transmitted light picture (i), fluorescent picture (ii), and vertical cross-section (iii) through the long axis of the cell after reconstructing the z-stack to generate a three-dimensional view (z-spacing is 0.5 μm; scale bar is 20 μm). (B) Micrograph of a cardiomyocyte in microchannel oriented parallel to the electric field between the microelectrodes; distances indicated as μm. (B′) illustration of an orthogonal cross-section (white line in Fig. 3 B). (C) Sketch illustrating a longitudinal cross-section (black line in Fig. 3 B) through the center of a microchannel. Unlimited diffusion in bath comprising the entire length of the microchannel with the ends of the channel extending ∼5 mm beyond each electrode (breaks indicated), thus comprising a volume of >5 nL. (D) Limited diffusion in bath comprising solely the area between the electrodes (40-μm wide, 250-μm long, and 10-μm high, ∼100 pL volume). Coverslip with microelectrodes (1), bath with cardiomyocyte (2), mineral oil (3), and microchannel in PDMS (4).