Sodium bicarbonate infusion increases discharge frequency of intrapulmonary chemoreceptors only at high CO 2

Abstract

We felt that earlier determinations of independent effects of extracellular pH and P CO 2 on intrapulmonary chemoreceptors (IPC) discharge frequency were difficult to analyze because they used perfused lungs, and ventilation-perfusion changes among parabronchi could not be controlled. We decided to repeat these studies in non-perfused lungs. We cannulated both extrapulmonary bronchi of 10 thoracotomized Pekin ducks anesthetized with sodium pentobarbital (25–35 mg/kg) and unidirectionally ventilated each lung. The perfused right lung mainteained gas exchange while the non-perfused left lung recieved 0.6 L/min of CO 2 mixed in air. We recorded the discharge frequency of one IPC per duck at various P CO 2 , re-established circulation, and infused 3.0 mmol/kg of sodium bicarbonate intravenously. After 15 min, discharge frequencies were again measured from the same IPC in the nonperfused lung. The slopes and intercepts of discharge frequencies vs ln P CO 2 relationship were depressed in six IPC, increased in two IPC and not significantly affected in two IPC. Arterial pH was increased significantly (0.11 unit) at 38 Torr arterial P CO 2 . We conclude that acutely increased extracellular sodium bicarbonate affects IPC discharge only by depressing sensitivity of most IPC to P CO 2 and does not have an independent effect through pH.