RYANODINE-INDUCED CONTRACTILE FAILURE OF SKELETAL MUSCLE

¹ Department of Pharmacology, Albany Medical College of Union University, Albany, New York

Rigor induced by ryanodine in the tibialis anticus muscle of the anesthetized cat in situ can be reduced or abolished by interfering with contractility of the muscle. A reduction in frequency of stimulation during the development of rigor induced by ryanodine considerably impaired progression of the rigor. Furthermore, ryanodine-induced rigor has been shown to be frequency-dependent. With the muscle contracting isometrically at a frequency of 0.2/sec, ryanodine induced a reduction of twitch height with little or no rigor. With highspeed recording to characterize the components of single twitches at low frequency, ryanodine reduced both the mean velocity of contraction and the time to peak tension. Some concepts are presented as a basis upon which either contractile failure or rigor of the same muscle can be explained.