The effect of potassium on carotid body chemoreceptor discharge in the anaesthetized cat.

1. In exercise the arterial plasma potassium rises; we have investigated the possibility that such rises might affect the carotid body chemoreceptor. 2. Intravenous infusions of KCl were used to produce hyperkalaemia in anaesthetized cats. 3. Intra-arterial catheter tip potassium electrodes were used to monitor changes in plasma potassium. 4. The effects of 5 min infusions of KCl on afferent carotid chemoreceptor preparations were studied. 5. Infusions of KCl, which produced increases in plasma potassium similar to those occurring in exercise in man, caused an initial large increase in mean firing frequency (237% of control). A phase of rapid adaptation of this response was followed by a phase of slower adaptation, but after 5 min of hyperkalaemia mean firing frequency was still significantly greater than control. The amplitude of the breath-by-breath oscillation in frequency appeared to increase in parallel with mean frequency so that the amplitude/mean ratio remained constant. 6. We conclude that plasma potassium changes during exercise may contribute to the chemical drive to breathe.