Membrane Ca2+ interactions and contraction in denervated rat soleus muscle

Abstract

Under voltage clamp conditions contractile responses and ionic currents of single fibres isolated from rat soleus, denervated for more than 20 days, were recorded in Na-free TEA containing solutions. The relationship between membrane potential and contraction has been analysed under various conditions. The addition of trivalent cations (La3+, Gd3+) resulted in a dose dependent reduction of the contractile response and similar effects were produced by polymyxin B (0.05-0.5 mM). By contrast in the presence of phospholipase D (1-5 U/ml) contractions were significantly increased for all values of depolarization. The time course of the change of tension amplitude after the application of Ca-free medium, was dependent on the amplitude, the duration and the frequency of the depolarization. Upon depolarization glycerol-treated fibres generated contractile responses which were similar to those recorded in normal muscle and were also dependent on [Ca]o. It is proposed that in denervated soleus muscle the negatively charged phospholipids at the outside of the membrane were involved in the depolarization-contraction coupling by means of their Ca binding properties. The quantity of Ca binding sites would be dependent on [Ca]o and membrane potential and their binding properties modified during and/or following variation in membrane potential.

Na+−Ca2+ EXCHANGE IN LIMB MUSCLES OF DYSTROPHIC (C57 BL/6J dy2J/dy2J) MICE

“…Recent experiments have demonstrated that the sarcolemmal calcium pool is involved in depolarization-contraction coupling of normal mammalian soleus (Sol) muscles (Leoty & Noireaud, 1987) and seems to play an important role in buffering calcium ions entering through the Na+-Ca2+ exchange (reverse mode) shown to be present in normal Sol muscle (Noireaud & Leoty, 1988). The presence of such an exchange explains why on exposure to Na+-free solution, normal slow-twitch Sol muscle generated contractile responses unlike normal fast-twitch iliacus muscle (Leoty, 1984).…”

EFFECT OF EXTERNAL SODIUM SUBSTITUTION ON POTASSIUM CONTRACTURES OF MAMMALIAN MUSCLES: POSSIBLE INVOLVEMENT OF SARCOLEMMA‐BOUND CALCIUM AND Na+‐Ca2+ EXCHANGE

“…The involvement of sarcolemmal calcium in depolarization-contraction coupling has been demonstrated recently in denervated soleus muscle of the rat (Leoty & Noireaud, 1987). In these experiments, external sodium ions were replaced by the monovalent cations Tris or tetraethylammonium (TEA+) to study changes in contractile activity.…”