Skeletal muscle ECF pH error signal for exercise ventilatory control

Pulmonary and Critical Care Unit, Massachusetts General Hospital and Harvard Medical School, Boston 02114; and Nuclear Magnetic Resonance Laboratory for Physiological Chemistry, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115 Evans, Allison B., Larry W. Tsai, David A. Oelberg, Homayoun Kazemi, and David M. Systrom. Skeletal muscle ECF pH error signal for exercise ventilatory control. J. Appl. Physiol. 84(1): 90-96, 1998. An autonomic reflex linking exercising skeletal muscle metabolism to central ventilatory control is thought to be mediated by neural afferents having free endings that terminate in the interstitial fluid of muscle. To determine whether changes in muscle extracellular fluid pH (pH e ) can provide an error signal for exercise ventilatory control, pH e was measured during electrically induced contraction by 31 P-magnetic resonance spectroscopy and the chemical shift of a phosphorylated, pH-sensitive marker that distributes to the extracellular fluid (phenylphosphonic acid). Seven lightly anesthetized rats underwent unilateral continuous 5-Hz sciatic nerve stimulation in an 8.45-T nuclear magnetic resonance magnet, which resulted in a mixed lactic acidosis and respiratory alkalosis, with no net change in arterial pH. Skeletal muscle intracellular pH fell from 7.30 ± 0.03 units at rest to 6.72 ± 0.05 units at 2.4 min of stimulation and then rose to 7.05 ± 0.01 units ( P