Cell transformation in isolated striated muscle of hydromedusae independent of DNA synthesis

Monotypical isolated and cultivated striated muscle was demonstrated to change (metaplasia) into a cell type possessing flagellae and other characteristics of smooth muscle cells [4]. In situ and within the first 48 h following isolation, no DNA synthesis is observed in striated muscle tissue. However, between the 2nd and 3rd day in culture, approximately one day prior to the formation of flagellae, a dramatic burst of DNA synthesis is observed. In the presence of low concentrations of mitomycin-C which inhibited DNA synthesis, the transformation process from striated to smooth muscle was virtually unaffected. Increasingly higher concentrations of mitomycin-C, which completely inhibited DNA synthesis yet inhibited flagellae formation when administered immediately following isolation, had only a graduated effect on flagellae formation which was inversely proportional to the length of time in culture before treatment, and the concentration employed. The results represent the first clear case of transformation of a differentiated cell type to another distinct type without going through the S phase of the cell cycle.     

Average electrostatic potential between the filaments in striated muscle and its relation to a simple Donnan potential.

An approximate analytical solution to the Poisson-Boltzmann equation for a cylindrical particle was used to calculate the relationship between the charge on the filaments and the average electrostatic potential. Both thick and then filaments were considered in the muscle lattice with a filament charge ratio of 4 to 1. Comparing this with a similar relationship obtained using simple Donnan theory showed a discrepancy at high charge where the Poisson-Boltzmann equation leads to saturation of the average potential. However, using two separate experiments from the literature, we have shown that at pH 7.0 muscle must not be close to saturation and thus is in a region of the curve where the two approaches agree.     

Regulatory proteins of lobster striated muscle.

The regulatory proteins of lobster muscles consist of tropomyosin and of troponin. Troponin contains a 17,000 chain weight component, two closely related components of about 30,000 and a 52,000 chain weight component. In addition to troponin, tropomyosin is required for the inhibition of the magnesium activated actomyosin ATPase activity in the absence of calcium and for the reversal of this inhibition by calcium. Lobster tropomyosin interacts with rabbit actin and lobster troponin interacts with rabbit tropomyosin. The 30,000 doublet component corresponds to the troponin-I of rabbit and inhibits the ATPase activity of actomyosin both in the presence and in the absence of calcium. The 17,000 component corresponds to the troponin-C of rabbit; it binds calcium and reverses the inhibition of the ATPase activity by troponin-I in the presence of calcium. No more than 1 mol of calcium is bound by a mole of troponin-C or by troponin. The 52,000 component interacts with tropomyosin and has been tentatively identified as troponin-T; however, it has not been demonstrated as yet that this component had a role in the regulation of lobster actomyosin.