Abstract
As far as we have been able to discover, there have been no published investigations of action potentials in heart muscle cultures. This is a report on a method which it is hoped will furnish information on the mechanism of irritable tissues in general and particularly those which are excited spontaneously.
In general, the potential difference between the micro-electrodes making contact with a muscle culture is impressed on the grid of a vacuum tube and measured by the deflection of a string galvanometer in the plate circuit.
The cultures were prepared by the usual hanging drop technique. Small pieces of the ventricle of 16-day rat embryos were explanted in a medium of rat blood plasma and rat embryo extract. The ages of the cultures varied from 2 days to 2 months. The present records were taken from the older cultures containing outgrowths of muscle which had differentiated in the manner described by Goss 1 and were presumably without nervous tissue elements. Spontaneous contraction occurs in practically all cultures at one time or another and may be rhythmic or irregular. There is a great variation in the duration of the resting and acting periods and also in the frequency of rhythmic activity.
The electrode systems are micro-pipettes, 2–5 mu in diameter at the tip, with chloride coated silver wire coils placed in the large ends and the whole filled with mammalian Ringer solution. These pipette electrodes are mounted in micro-manipulators 2 and enter the moist chamber, on which the culture cover slip is placed, through a water trap as used by Chambers. 3 Such an electrode system has a high electrical resistance which precludes the direct use of a rapid recording instrument even if polarization difficulties could be overcome. The electrodes are connected to the grid circuit of a type 32 vacuum tube, operating at its free grid potential so as to draw a minimum of grid current.
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