Fig. 2.

Compartmentalization of NAD+ pools in skeletal muscle. Diagram of a striated skeletal muscle fiber. NAD+ is localized to mitochondrial, nuclear, cytosolic, and membrane proximal pools in muscle cells. Additional NAD+ compartments not diagrammed here include vesicular compartments. The NAD+/NADH ratio is higher in the nuclear and cytosolic compartments compared to the mitochondrial compartment. The ratio is unknown in the membrane proximal compartment in muscle. Enzymes that consume NAD+ and their relative subcellular localizations are found within black or white boxes. Integrin receptors and membrane channels that transport NAD+ and calcium across the sarcolemma can be seen in the diagram