The objectives of the proposed study include correlation of the myofilament lattice structure of striated muscle with the physiological events of muscle contraction by low-angle X-ray diffraction, electron microscopy, light microscopy and physiological techniques. Experiments are designed to: (a) identify and investigate the forces (long-range electrostatic, van der Waals's, Donnan-osmotic, and contractile forces and perhaps entropic factors) between the myofilaments which are responsible for the maintenance of the hexagonal array, interfilament distance, and lattice stability in the intact and skinned striated muscle fiber; (b) further define the colloidal properties of liquid-crystalline systems composed of large macromolecules and the relationship of such systems to the myofilament lattice of striated muscle; (c) determine the relation between the interfilament spacing and lattice stability during rest and rigor as well as during active tension in skinned muscle fibers and intact muscle fibers. Attainment of these specific goals will permit the evaluation of the basic premise that the A-band lattice may be liquid-crystalline in nature and, if so, define precisely the equilibrium states of such a structure. In addition the role of the sarcolemma as it regulates the Donnan-osmotic forces and the contribution of these forces to lattice stability in intact and skinned fibers will be defined. This study elucidates a role of liquid crystals in functioning biological systems.