Mechanical noise of the myocardium as an index of sarcoplasmic reticulum activity

The effects of caffeine (0.5-12 mM) and cooling on the mechanical noise (MN) and relaxation rate of contractile response (RR) were studied in experiments on rat papillary muscles. Mean frequency of MN and RR were found to have similar temperature dependences from 12 to 32 degrees C. MN amplitude was more sensitive to the action of sarcoplasmic reticulum activity blocker, caffeine, than RR one. MN as an index of sarcoplasmic reticulum activity made it possible to demonstrate a competition between caffeine and local anaesthetics described earlier for skeletal muscles.