Studies on the adaptation rate and frequency distribution of type A and type B atrial endings in cats.

Since from the study of location no clue could be found regarding the difference in discharge patterns of type A and type B endings in cats, two separate series of experiments were performed. In the first series, the responses obtained from types A, B and intermediate endings on stretching the isolated atrial chamber were identical. From the second series directed to the frequency distribution of atrial endings and performed by recording of the neural activity in single fibres of the whole vagus, a ratio of 1:1 between type A and type B endings was found. Endings with an intermediate pattern of discharge were rare. Out of 71 atrial endings recorded from 4 vagus nerves, only 7 were of this type. These studies showed that: (1) the types A, B and intermediate endings are slowly adapting, (2) the intermediate type is a variant of type B and (3) type A and type B endings belong to different types. It is speculated that the difference in discharge patterns of type A and type B endings may be due to their arrangements in the atria.