Effect of insulin on characteristics of contractile responses of fast and slow skeletal muscles of rats with acute streptozotocin-induced diabetes

Comparison of amplitude-time characteristics of fast (m. EDL) muscles in rats with acute model of streptozotocin diabetes (SD) (12 and 30 days after treatment with streptozotocin) did not reveal significant changes in strength of single normalized contractile responses as compared with control. In slow (m. Soleus) muscles of rats with the 30-day SD there were observed essential changes in amplitude-time characteristics of such contractile responses: a decrease of their amplitude and an increase of duration. In diabetic rats treated with a course of insulin, resistance of skeletal muscles to both types of exogenous insulin is developing. Both in control and in diabetic animals the fatiguing stimulation of m. EDL by firing from 5 impulses did not reveal significant differences at early (up to 3 min) terms of development of fatigue. Under similar conditions, fatigue of m. Soleus in rats of both diabetic groups developed significantly faster as compared with control (as early as 30 s after the beginning of stimulation). Insulin at a concentration of 5-1 nM produced a dose-dependent decrease of amplitude of single contractile responses in fast and slow muscles of rats with the acute SD model (the negative inotropic action). The same effect of insulin, but at the higher concentrations, we demonstrated earlier in health rats. Insulin at a concentration of 10 nM did not produce essential effect on the time course of depression of responses in the course of development of fatigue at tetanic stimulation of m. EDL and m. Soleus both in control and in diabetic rats, but affected essentially the time course of change in duration of the half-decline (T(hd)) of their tetanic responses. The presence of insulin in the bath solution led to stabilization of the muscle relaxation period in the course of development fatigue in all studied animal groups.