Contractions of skinned cardiac cells elicited by current pulses

Cardiac muscle fragments with disrupted sarcolemma were prepared by homogenization of mouse ventricles. The preparations exhibited spontaneous contractions of a rate between 3 min-1 and 12 min-1 at 20 degrees C, when they were kept in an appropriate solution. 2. Fragments of about cellular size were attached to two stiff glass microelectrodes, and additional contractions between the spontaneous beats were elicited by current pulses. The duration and intensity of the stimuli were varied to obtain strength-duration curves. Rheobase was in the range of 1.5 muA to 10 muA (no isolation of surrounding bath), chronaxia at 35 degrees C between 30 ms and 80 ms. 3. One microelectrode could be glued to a photodiode-force-transducer for simultaneous recording of contractions and electrical stimulation or potential measurement. Duration of phasic contractions was nearly 1s, force was up to 4muN (20 mN/mm2 of tension).