title: 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.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D005990:Glycerol / Q000494:pharmacology; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009121:Muscle Denervation; D009132:Muscles / Q000166:cytology / Q000502:physiology*; D010739:Phospholipase D / Q000494:pharmacology; D011112:Polymyxin B / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012508:Sarcolemma / Q000187:drug effects
chemical_list: D007811:Lanthanum; D010739:Phospholipase D; D011112:Polymyxin B; D005990:Glycerol; D002118:Calcium