In vitro toxicity screening using cultured rat skeletal muscle cells. II. Agents affecting excitable membranes

The screening of chemicals for their potential to interfere with excitable cell membranes should be an important element of in vitro testing for acute toxicity. The suitability for this purpose of a test system using primary cultured rat skeletal muscle cells was evaluated. The test protocol involved the determination of the concentration-dependent effects on three endpoints: (1) spontaneous contractility, (2) membrane integrity and (3) energy metabolism. The chemicals investigated were: NaCl, KCl and CaCl(2); cardiac glycosides (ouabain, digoxin); sodium channel toxins (tetrodotoxin, saxitoxin, veratridine, Anemonia sulcata toxin II, Bolocera tuediae toxin II); an acetylcholine agonist (carbachol); a calcium antagonist (D600) and three membrane-directed insecticides (deltamethrin, DDT, lindane). The response pattern of most of these substances-alteration of contractility at concentrations that neither affected the energy metabolism nor were cytolethal-characterized them as acting either on the excitable membrane or on the excitation-contraction coupling and the contractile apparatus. The results indicate that the test system is suited to assess chemical effects resulting in: (i) changes of resting membrane and threshold potentials, (ii) altered sodium channel function, (iii) opening of endplate channels, (iv) blockade of calcium channels, and (v) inhibition of Na(+)/K(+)-ATPase.