HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Thompson, C. H Articles by Radda, G. K Search for Related Content PubMed Articles by Thompson, C. H Articles by Radda, G. K

Triiodothyronine-induced changes in proton efflux from rat skeletal muscle in vivo

Thompson CH, Kemp GJ, Radda GK. Triiodothyronine-induced changes in proton efflux from rat skeletal muscle in vivo. Eur J Endocrinol 1995;133:260–4. ISSN 0804–4643

Hyperthyroidism is associated with muscle weakness, abnormal aerobic metabolism and increased lactate production. Muscle cell acidification during exercise is reduced, suggesting abnormally increased proton efflux. Using ³¹P magnetic resonance spectroscopy to measure cell pH and phosphocreatine concentration, we quantified effective proton efflux from rat leg muscle in vivo following 10-Hz sciatic nerve stimulation in seven rats injected with triiodothyronine (T₃) for 5 days and in 11 controls. Proton efflux during recovery was sigmoidally pH-dependent in both groups but the initial proton efflux rate did not differ (16 ± 3 mmol·kg^–1 · min^–1 in treated animals vs 15 ± 1 mmol·kg^–1·min^–1 in controls), despite a significantly smaller pH change from basal in treated animals (0.60 ± 0.04 vs 0.78 ± 0.03 in controls, p = 0.002). The pH dependence of proton efflux can be characterized by an apparent K_m, defined as the pH below basal at which proton efflux rate falls to half its start-of-recovery value. This K_m was smaller in the T₃-treated group (0.44 ± 0.04 vs 0.59 ± 0.03 in controls, p = 0.02). This suggests an increased affinity for protons by cell membrane proton transport processes such as the sodium–proton antiporter and may explain some of the metabolic changes seen clinically in hyperthyroid skeletal muscle.

CH Thompson, MRC Biochemical and Clinical Magnetic Resonance Unit, Oxford Radcliffe Hospital Trust, Headington, Oxford OX3 9DU, UK