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Abstract: The rate of Ca2+ accumulation in the sarcoplasmic reticulum of the skeletal muscle (m. gastrocnemius lateralis, m. vastus medialis, andm. soleus) is studied in rats under conditions of functional off-loading of the hind paws (suspending animals by the tail). The rate of Ca2+ transport in the sarcoplasmic reticulum is shown to be stepped up in all these muscles. In the sarcoplasmic reticulum ofm. gastrocnemius lateralis andm. vastus medialis the Ca2+ transport rate reliably drops, which does not occur inm. soleus. During a 2-week period of readaptation of animals suspended for 40 days, the Ca2+-transporting function of them. soleus sarcoplasmic reticulum gradually recovers to reach the control values, whereas the time course of recovery of Ca2+-pump activity in the sarcoplasmic reticulum ofm. gastrocnemius lateralis andm. vastus medialis has a phasic pattern.

Abstract: The rate of Ca2+ accumulation in the myocardial sarcoplasmic reticulum is studied in experiments on rats under conditions of hind paw functional off-loading by suspending animals by the tail for 1 to 40 days, as well as during a 2-week period of readaptation after a 40-day load relief. The rate of Ca2+ transport in the myocardial sarcoplasmic reticulum reliably drops (by 33%) after 40 days of suspension. At earlier stages of off-loading Ca-pump activity in the sarcoplasmic reticulum does not change reliably. After resumption of the loads in animals suspended for 40 days, the transporting function of the myocardial sarcoplasmic reticulum rapidly reverts to the control level, which is indicative of a reversible pattern of load relief-induced changes in the rate of Ca2+ transport.