Collagen gels populated with rat neonatal heart cells can be used for optical recording of rhythmic contractions which also show ECG-like potentials.

Neonatal heart cells populated collagen gels show rhythmic contractions which can be recorded optically and electrically. Optical recordings revealed two populations of rhythmically contracting gels: 1) highly coherent contracting collagen gels with normally distributed contraction interval times and contraction amplitudes, and 2) irregularly contracting gels with a multi-modal distribution of contraction interval times and amplitudes. The irregularly contracting gels were shown to be 'semi regular', which means that a short contraction interval was preferentially followed by another short interval. The volume of the collagen gel during the contraction decreased, and our calculations indicate that the myocytes expel 3-10 times their own volume from the gel. Changes in electrical potential were observed depending on the location of the electrodes. These electrical, ECG-like changes in potential were maximal when one electrode was placed in the centre and the other at the edge of the gel. The results of this study indicate that myocyte-populated collagen gels are a very promising system for studies of electrophysiology and coherent contractions.