TY - JOUR T1 - The effect of aminophylline on function and intracellular pH of the rat diaphragm JF - European Respiratory Journal JO - Eur Respir J SP - 991 LP - 996 DO - 10.1183/09031936.93.03090991 VL - 3 IS - 9 AU - CD Shee AU - AM Wright AU - IR Cameron Y1 - 1990/10/01 UR - http://erj.ersjournals.com/content/3/9/991.abstract N2 - We studied the effect of aminophylline on twitch tension (TT) and intracellular pH (pHi) in isolated rat diaphragm strips that were fatigued, hypercapnic, or hypoxic. Superfused muscles were directly stimulated at 0.5 Hz. The pHi was measured from distribution volumes of dimethyl-oxazolidinedione. Fatigue was induced by intermittent tetanic stimulation. Hypercapnia and hypoxia were produced by altering superfusate carbon dioxide tension (PCO2) or oxygen tension (PO2). Aminophylline (1.0 mmol.l-1) reversed the twitch decay seen during fatigue or hypercapnic acidosis, and caused partial recovery of twitch depression during hypoxia. Muscle fatigue was not due to an intracellular acidosis. Both hypercapnia and hypoxia lowered pHi. Aminophylline did not alter pHi in unstimulated muscles, but caused a significant fall in pHi in stimulated muscles that were fatigued or hypoxic. High dose aminophylline improved twitch tension in diaphragm strips that were fatigued, acidotic, or hypoxic. Twitch potentiation was not due to an intracellular alkalosis. Aminophylline lowered pHi in stimulated muscle, and thus, theoretically, could sometimes be harmful in the treatment of muscle fatigue. ER -