Comparison between the delayed outward current in slow and fast twitch skeletal muscle in the rat.

Publisher Website
Google Scholar
Abstract
A comparison of the delayed outward current of isolated fibers from rat soleus and iliacus muscle was made using a double sucrose-gap voltage-clamp method. The fast and slow components of the outward current were separated using time constants of the tail currents. In both iliacus and soleus fibers there is a shift in reversal potential which depends on the quantity of current that flows during depolarization. The shift is larger in iliacus than in soleus; it is absent in glycerol-treated muscles. The results obtained in normal and in detubulated fibers show that the shift is due to an accumulation process of K+ in the lumen of the T-tubules. In detubulated soleus fibers the outward current is composed of a fast and a slow component, each with the same reversal potential; in detubulated iliacus the slow component is absent. In both types of muscles TEA [tetraethylammonium] produces a dose-dependent block of the total outward current. 4-Aminopyridine has different effects; it inhibits the total outward current in iliacus fibers and only the fast component in soleus fibers. Apparently in soleus fibers a fast and a slow component participate in the K outward current, while only a fast component is present in iliacus muscle.