Time-resolved x-ray study of effect of sinusoidal length change on tetanized frog muscle

Time-resolved x-ray diffraction studies were done on frog skeletal muscles with synchrotron radiation by applying sinusoidal length changes of frequency 10 Hz and amplitude approximately 1% to isometrically contracting muscles at approximately 17 degrees C. Distinct periodic intensity changes were observed in the 14.3-nm myosin meridional reflection and the equatorial 1,0 and 1,1 reflections. Response of the 14.3-nm reflection to the sinusoidal length change was nonlinear, as evidenced by a large second harmonic in its oscillatory intensity change, whereas the response of the equatorial 1,1 reflection was closely linear, as evidenced by almost sinusoidal intensity change. Intensity change of the 1,0 reflection was nearly antiphase to that of the 1,1 reflection. Integral widths of the 14.3-nm meridional reflection measured along the meridian and of the equatorial 1,1 reflection remained almost constant during tension development, while that of the 1,0 reflection tended to decrease. The widths of the 14.3-nm meridional reflection perpendicular to the meridian and of the equatorial 1,0 reflection appeared to undergo oscillatory changes in response to the sinusoidal length changes.