The effects of lanthanum on electrical and mechanical events in mammalian cardiac muscle.
1. The effects of various concentrations of lanthanum (La3+) on the force of contraction and on action potentials was investigated in isolated papillary muscles of the guinea-pig. 2. The force of contraction was initially reduced by La3+. During long exposure to high concentrations (i.e. 50, 100 and 500 muM) the contraction amplitude was increased again and a rise in resting tension was observed. These late changes in force of contraction also occurred after short exposure to 500 muM La3+ (2 min) when La3+ had been removed from the medium. 3. The action potentials were shortened at 20% of repolarization (plateau level) during La3+ exposure, whereas at 90% of repolarization a transient prolongation was observed. The resting potentials were reduced only at high concentrations and long duration of exposure. 4. 500 muM La3+ reduced the force of contraction to the control value obtained before addition of ouabain (5x10(-7)M). The ouabain-induced shortening in action potential duration at the plateau level was not reversed by the same concentration of La3+. 5. It is concluded that the action of La3+ on cardiac muscle cannot be explained by a simple displacement of superficially bound calcium. The characteristic effects observed at high concentrations reduce the value of La3+ as a pharmacological tool used in the study of calcium turnover.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology*; D008297:Male; D008839:Microelectrodes; D009200:Myocardial Contraction / Q000187:drug effects; D010210:Papillary Muscles / Q000502:physiology; D013997:Time Factors
D007811:Lanthanum