Each of the images in our gallery shows the relative position of the indicated proteins in that cell. In all cases the proteins are distributed in discrete locations either on the plasma membrane or within the membrane of an intracellular organelle. One protein has been labelled with fluorescein and is pseudo-coloured green, the other was labelled with Texas Red and is pseudo-coloured red. If the two proteins had identical 3D co-ordinates then it appears as a white square, otherwise the square remained red or green (if only one of the proteins was located at that spot), or black if neither protein was located at that position. If the proteins are together then they are within 100 nm of each other in X and Y (perpendicular to the optical axis of the microscope) and within 250 nm of each other in Z (along the optical axis).

In the cases of smooth and cardiac muscle, all of the labelled proteins have been implicated, either directly or indirectly, in regulating the intracellular calcium concentration, which is critical in controlling the force with which a muscle contracts. If the proteins are co-distributed then they may be functionally coupled, a lack of co-distribution indicates that they are functionally isolated from each other.

Take a look at the digital images of smooth and cardiac muscle and arterial endothelium.