Carbon dioxide and acid base balance in the isolated rat diaphragm

A method for measuring the net acid base exchange in an isolated rat diaphragm preparation is described. Particular attention is paid to monitoring the functional status and maintaining optimal diffusion conditions. A steady net acid efflux of the order of 250 n mole/g·min is found in the resting state. This increases following a series of isometric contractions. In the resting state the total measured lactate + pyruvate efflux was found to be less than the net acid efflux. The net acid efflux increases following a sudden decrease inpCO₂ and decreases or reverses following a sudden increase inpCO₂ or a decrease in external bicarbonate. The net base loss during a period of 1 h following the exposure to high (20%) CO₂ represents a large fraction of the predicted total bicarbonate generated within the fibres by non-bicarbonate buffers. This indicates that the effects of intracellular non-bicarbonate buffers can be transmitted to the external solution following a change inpCO₂. The most plausible explanation is that passive bicarbonate ion movements are responsible. Values of the ‘apparent \(P_{{\text{HCO}}_{\text{3}} }\) ’ have been calculated and vary under different conditions from a value of 1.3×10⁻⁷ to 1.9×10⁻⁶ cm·s⁻¹.