Impact of buffering hypercapnic acidosis on cell wounding in ventilator-injured rat lungs

Abstract

We measured the effects of raising perfusate pH on ventilator-induced cell wounding and repair in ex vivo mechanically ventilated hypercapnic rat lungs. Lungs were randomized to one of three perfusate groups: 1) unbuffered hypercapnic acidosis, 2) bicarbonate-buffered hypercapnia, or 3) tris-hydroxymethyl aminomethane (THAM)-buffered hypercapnia. The membrane-impermeant label propidium iodide was added to the perfusate either during or after injurious ventilation providing a means to subsequently identify transiently wounded and permanently wounded cells in optical sections of subpleural alveoli. Normalizing perfusate pH in hypercapnic preparations attenuated ventilator-induced cell injury, particularly in THAM-buffered preparations. This was observed despite greater amounts of edema and impaired lung mechanics compared with other treatment groups. Protective effects of buffering of hypercapnic acidosis on injury and repair were subsequently confirmed in a cell scratch model. We conclude that buffering of hypercapnic acidosis attenuates plasma cell injury induced by mechanical hyperinflation.

Fig. 1.

Experimental protocol. PI, propidium iodide; THAM, tris-hydroxymethyl aminomethane.

Fig. 2.

Box plots of number of PI-positive cells per alveolus (PI/Alv) by treatment group. Refer to text for explanation of A and B subgroups. *P < 0.05 compared with corresponding Krebs group (i.e., THAM A compared with Krebs A, bicarbonate B compared with Krebs B, and THAM B compared with Krebs B). The line within the boxes represents the mean values.

Fig. 3.

A549 cell scratch model with data points. Percentages of plasma membranes with permanent wounds as determined by PI staining. Buffering was associated with fewer permanent wounds, suggesting protective effects on cellular repair following injury. The line within the boxes represents the mean values. *P < 0.05 compared with unbuffered acidosis. Unbuff, unbuffered; Normocap, normocapnia.