THE EFFECT OF APPLIED MECHANICAL VIBRATION ON 2 DIFFERENT PHASES OF RAT PAPILLARY-MUSCLE RELAXATION

Applying external mechanical vibration during the relaxation phase of rat papillary muscle decreases the duration of the first part of the r elaxation phase. To elucidate the basic mechanism responsible for this shortening of the relaxation period, we applied a controlled vibratio n to isolated twitching rat papillary muscles during various phases in the relaxation of a twitch. The first part of the relaxation phase wa s accelerated when length perturbations were applied in the first part of the relaxation of a twitch, dependent on both amplitude and freque ncy of the perturbation. When vibrations were applied in the first hal f of the relaxation, the second phase of relaxation was slightly slowe r (about 20%), but when no vibrations were applied in the first phase, relaxation could be accelerated by applying vibration in the latter h alf of the relaxation phase. Thus, in the latter half of relaxation, t he acceleration of relaxation depended upon perturbation events earlie r during that twitch. This study indicates that vibration-induced acce leration of relaxation is due (at least in part) to an apparent increa se in detachment rate of attached cross-bridges from the thin filament without substantial reattachment.