The afferent discharge pattern of atrial mechanoreceptors in the cat during sinusoidal stretch of atrial strips in situ.

1. The differences in spike discharge from atrial mechanoreceptors in vivo suggest the existence of different receptor types. To test this possibility, and to see how atrial receptors compare with other mechanoreceptors, their response was studied under comparable stimulus conditions.2. Sinusoidal length changes, with frequencies from 1 to 10 Hz and amplitudes of 1.5-5.0 mm at a given static extension, were imposed in situ on strips of atrial receptor areas of cats.3. The receptor response was evaluated from functional single fibres in terms of number of spikes per stimulus period, average discharge rate, instantaneous spike frequency, and phase angle between forcing function and instantaneous frequency.4. Irrespective of the fibre type, atrial fibres appear to originate from identical mechanoreceptors which sense length at low stimulus frequency and low stimulus amplitudes, but also sense velocity in the high frequency range and with large stimulus amplitudes.5. The difference in the discharge pattern and in the functional behaviour of the atrial fibres in vivo can be explained on the basis of identical receptors.6. The difference in the temporal occurrence of the atrial burst is still open to debate, but probably is related to the site of the receptor.