Metabolite diffusion in giant muscle fibers of the spiny lobster Panulirus argus.

The time- and orientation-dependence of metabolite diffusion in giant muscle fibers of the lobster Panulirus argus was examined using (31)P- and (1)H-pulsed-field gradient nuclear magnetic resonance. The (31)P resonance for arginine phosphate and the (1)H resonances for betaine, arginine/arginine phosphate and -CH(2)/-CH groups were suitable for measurement of the apparent diffusion coefficient, D. Diffusion was measured axially, D(//), and radially, D( perpendicular ), in fibers over diffusion times of 20 to 300 ms. Diffusion was strongly anisotropic, and D(//) was higher than D( perpendicular ) at all times. Radial diffusion decreased with time until a steady-state value was reached at a diffusion time of approximately 100 ms. Changes in D( perpendicular ) occurred over a time scale that was consistent with previous measurements from fish and mammalian muscle, indicating that diffusion is hindered by the same types of barriers in these diverse muscle types. The time dependence indicated that the sarcoplasmic reticulum is the principal intracellular structure that inhibits mobility in an orientation-dependent manner in skeletal muscle. The abdominal muscles in P. argus are used for anaerobic, burst contractions during an escape maneuver. The fact that these muscle fibers have diameters that may exceed hundreds of microns in diameter, and nearly all of the mitochondria are localized near the sarcolemmal membrane, suggests that barriers that hinder radial diffusion of ATP equivalents may ultimately limit the rate of post-contractile recovery.