No abstract

SummaryMyosin from molluscan adductor muscle is regulated directly by Ca2+ binding. In the absence of Ca2+ the ATPase activity is greatly inhibited. We review the application of transient kinetic methods to this system and show how they can be simple to perform and less ambiguous than steady-state methods.

Four major inorganic cations --Na +, K--, Mg 2+ and Ca 2+ contribute mainly to the regulation of activity of muscle cells. The aim of the present comparative study was fo reveal the principal factors which determine the great variety of the cationic contents in different muscles of various animais. Functionally distinguished muscles of 70 species of marine, freshwater and terrestrial animals of 6 types of metazoans were investigated. The analysis of this muscle variability in regulation to the intracellular cati, onic contents has confirmed the qualitative heterogeneity of the muscle fibre populations investigated. The data obtained have permitted a subdivision of the latter into some definite groups, depending on the ionic composition of the extracellular fluids (environmental factor) as well as on the direction and the level of the functional specialization of muscles (inherent factor). In general a linear reciprocal relationship between [K+]i and [Na+]i in different skeletal muscles of various species was observed. In the saine organism an acceleration of a contractile response of the muscles is associated with an increase of a cellular selectivity of K § as compared to Na+; (SK/Na) -V c = A + B/SK/N,~. The character of this relation (the value of B) is species specific and reflects the level of development of a locomotory activity of the animais. At the same time the results obtained enable us to draw the conclusion that the trends in the cationic parameters in muscles do not coincide with the general course of the animal evolution. Itis demonstrated that the interrelation between functional (contractile) properties of skeletal muscles and cationic distribution patterns can be used as an 'ionic testing' method in medical-biological practice for diagnosing the physiological state of muscles. The results are discussed in terms of the physiological significance of inorganic cations involvement in the intracellular information transmission.