EFFECTS OF BATRACHOTOXIN ON CAT PAPILLARY-MUSCLE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 196  (2) , 433-444
Abstract
The effects of batrachotoxin [BTX, a steroidal alkaloid from the skin of Phyllobates aurotaenia] upon the contraction and transmembrane potential of cat right ventricular papillary muscles were studied in vitro at 37.degree. C. BTX (2.0 .times. 10-9 M) increased isometric contractile force by about 50% from control force, decreased the potential difference across the cell membrane to approximately -50 mV and produced spontaneous contractions of the papillary muscles. Each BTX-induced spontaneous contraction was accompanied by a spontaneous action potential which was generated when an oscillation in membrane potential reached threshold level. Spontaneous activity occurred only in muscles which were previously stimulated electrically. The positive inotropic effect of BTX was accompanied by an increase in the rate of force development. Papillary muscles from cats pretreated with reserpine did not differ from normal muscles in their responses to BTX treatment. Tetrodotoxin (2.0 .times. 10-7 M) antagonized the effects of BTX, a finding which suggests that the actions of BTX are mediated by a selective increase in membrane permeability to Na+. The resultant BTX-elicited increase in the intracellular Na+ concentration may increase the force of contraction through an augmentation of Ca influx via the Na-Ca exchange system.