MAGNETIC STIMULATION OF FERRET PAPILLARY-MUSCLE

1. Ferret papillary muscles were magnetically stimulated by the discha rge of a capacitor through an inductance. 2. An induced current densit y of 39 mA cm(-2) averaged over 280 mu s (=11 mu C cm(-2)) corresponde d to threshold. 3. A short galvanic current pulse was found to have a comparable charge threshold. 4. The time-varying magnetic field or the magnetically induced electrical field did not result in excitation un less current was allowed to flow. 5. Threshold conditions could be rea ched by adding subthreshold magnetically induced current to subthresho ld galvanic current. A suprathreshold galvanic current could be preven ted from exciting by simultaneously applying induced current of opposi te direction. 6. It is concluded that outward current through the memb rane capacity is the stimulus, independent of the origin of the curren t.