title: The tension-depolarization relationship of frog atrial trabeculae as determined by potassium contractures.
abstract: 1. In the presence of extracellular Na ions K contractures evoked from isolated frog atrial trabeculae show an initial phasic and a subsequent tonic contractile response. 2. The phasic response shows a steep dependence on membrane potential, persists in Na-free fluid, but is blocked by Mn ions, D600 and tetracaine. It has an indirect dependence on the [Ca]0 and would seem to be associated with both the secondary inward current and the release of Ca2+ from intracellular stores. 3. The tonic component of the K contracture is unaffected by D600 or tetracaine, shows a shallow dependence on membrane potential but is absent in Na-free fluid. Its tension-depolarization curve is immediately affected by alteration of either the [Ca]0 or the [Na]0. The form of the tension-depolarization relationship and the effects of [Ca]0 and [Na]0 are consistent with the strength of the tonic tension being determined by a 3Na+ for 1Ca2+ exchange across the cell membrane. 4. The results agree well with those obtained previously with voltage-clamp experiments on the same tissue, and may also help with the interpretation of Ca-flux experiments.
mesh_terms: D000818:Animals; D016275:Atrial Function; D002118:Calcium / Q000494:pharmacology; D005711:Gallopamil / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D008345:Manganese / Q000494:pharmacology; D008564:Membrane Potentials; D009200:Myocardial Contraction / Q000187:drug effects; D011188:Potassium / Q000502:physiology*; D011894:Rana pipiens; D012964:Sodium / Q000494:pharmacology; D013748:Tetracaine / Q000494:pharmacology
chemical_list: D013748:Tetracaine; D005711:Gallopamil; D008345:Manganese; D012964:Sodium; D011188:Potassium; D002118:Calcium