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

Abstract

SUMMARY1. A comparison of the delayed outward current of isolated fibres from rat soleus and iliacus muscle has been made using a double sucrose-gap voltage-clamp method.2. The fast and slow components of the outward current were separated using time constants of the tail currents. The results indicate that in both iliacus and soleus fibres there is a shift in reversal potential which depends on the quantity of current that flows during depolarization.3. The shift is larger in iliacus than in soleus; it is absent in glycerol-treated muscles.4. The results obtained in normal and in detubulated fibres show that the shift is due to an accumulation process of potassium ions in the lumen of the T-tubules.5. In detubulated soleus fibres 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. 6. In both types of muscles TEA produces a dose-dependent block of the total outward current. 4-aminopyridine has different effects; it inhibits the total outward current in iliacus fibres and only the fast component in soleus fibres.7. These results show that in soleus fibres a fast and a slow component participate in the potassium outward current, while only a fast component is present in iliacus muscle.

Asymmetric charge movement in contracting muscle fibres in the rabbit.

“…This simple effect of sucrose provides an explanation for the more negative V and smaller k found in previous charge movement experiments using sucrose compared to those without it, in both mammals (Hollingworth & Marshall, 1981;Dulhunty & Gage, 1983;Simon & Beam, 1985 a, b) and amphibia (Adrian & Almers, 1976;Almers & Best, 1976;Chandler et al 1976a;Campbell, 1983;Hui, 1983). Similarly, it can account for the slower time course of the potassium tail currents observed in rat skeletal muscle by Duval & Leoty (1980) using a Ringer solution, compared to that seen by Beam & Donaldson (1983) using a hypertonic sucrose solution. The magnitude of the sucrose effects depended on the concentration added; in this study 290 mM-sucrose produced greater effects than 80 mM-sucrose.…”

A patch‐clamp study of delayed rectifier currents in skeletal muscle of control and mdx mice.

“…The apparent inactivation process could be partly due to an accumulation of potassium ions in the tip of the pipette, which would decrease the driving force and the ionic current with time. Alternatively, it could result from the presence of two different types of channels, both participating in the macroscopic delayed rectifier channels, each with its own characteristic inactivation time constant (Duval & Leoty, 1980;Brinkmeier, Zachar & Rudel, 1991). To check for these possibilities, the kinetics of the ionic current were A assessed directly using a patch that had a small number of channels.…”

Fiber Types in Mammalian Skeletal Muscles

“…During slowto-fast phenotype transition, the BK channels of soleus acquire properties similar to those of FDB. Finally, potassium delayed outward current differs between fast and slow fibers of the rat: two components (one slow and one fast) are detectable in slow fibers, whereas only the fast component is present in fast fibers (195). D) SODIUM CHANNELS.…”