The effect of potassium and venous CO2 loading on chemoreceptor firing in anaesthetized cats

The CO2 production of 5 anaesthetized cats, ventilated to a constant PaCO2 and PaO2 by appropriate alteration of tidal volume and FIO2, was altered by means of an extracorporeal gas exchanger. Afferent chemoreceptor discharge was recorded from a single fibre preparation of the right carotid sinus nerve and the respiratory oscillations in firing were derived over 50 breath (2.5 min) periods. In response to an approximate doubling of CO2 production the discharge oscillation showed an increase in amplitude (P less than 0.05) but no change in mean level. When KCl was infused to produce a mean arterial [K+] of 5.9 mmol/L, while maintaining the same level of CO2 loading, the amplitude of the oscillation increased from 2.9 +/- 0.5 impulses/sec to 5.2 +/- 1.0 impulses/sec (P less than 0.05) and the mean increased from 2.6 +/- 0.4 impulses/sec to 3.9 +/- 0.2 impulses/sec (P less than 0.01). The implications of these findings are discussed.