Attenuation of ultrasound in homogenates of bovine skeletal muscle and other tissues

Abstract

The attenuation of ultrasound in homogenates of bovine skeletal muscle and suspensions of myofibrils was measured over the frequency range 1.5–7 MHz, and found to be proportional to protein concentration in both. In the homogenates it varied with frequency and temperature in a similar way to the attenuation in post rigor muscle tissue; myofibrils showed a higher frequency dependence. The attenuation in homogenates of bovine muscle, liver and kidney and in suspensionsof myofibrils was measured over the pH range 3.5–13, and each showed a peak at about pH 11.5. This was thought to be due to a proton transfer process between NH 3 + groups on the tissue proteins and OH − ions in the suspending fluid. A substantial peak at about pH 5 in the muscle and myofibril suspensions was not observed in homogenates of liver and kidney and was thought to be due to components of muscle that are absent from the other tissues. Myofibrils suspended in percoll solution of density 1.05 g cm −3, chosen to match approximately the density of the myofibrils, showed a slightly lower attenuation over the pH range 5–7, but a pH dependence similar to that of the myofibrils suspended in saline. The difference in the attenuations may be interpreted as the viscous component of the attenuation due to relative motion between the myofibril and its surrounding saline. The peak at pH 5 did not, however, appear to be due to the viscous loss mechanism peaking due to maximum shrinkage (and therefore maximum density) of the myofibril near this pH. The attenuation in homogenates of muscle was decreased by suspending in 0.5 M or 1.0 M rather than 0.1 M KCl. This may have been caused by the myosin filaments dissolving at high ionic strength.