Potentiation by endotoxin of responses associated with increases in calcium conductance

Bacterial endotoxin at concentrations of 0.03 mug/ml enhanced the following responses, each of which reflects calcium influx: (1) contraction of spiral intestine retractor muscle of dogfish; (2) amplitude of postsynaptic potential of squid giant synapse as a function of presynaptic depolarization; (3) membrane responses of deep abdominal extensor muscle of crayfish, stimulated intracellularly; and (4) slow transient (calcium) current in trabeculae of frog atrium under voltage clamp. Corticosteroid antagonized the endotoxin effect on the smooth muscle, not on the frog atrial current. One mechanism of action of endotoxin may be to increase transmembrane calcium currents.