Effect of hormonal and substrate backgrounds on cell membrane function in normal males

Hormonal and substrate influences on in vivo cellular membrane function were evaluated in 15 healthy male volunteers. Each subject underwent serial evaluations of membrane function in the anterior tibialis muscle, as assessed by transcutaneous measurement of resting membrane potential (E(m)). Group A subjects (n = 9) underwent measurement of resting E(m) in the basal state and again during the 10th day of intravenous feeding (IVF). Group B subjects (n = 6) underwent measurement of resting E(m) in the basal state during epinephrine infusion and again during epinephrine infusion on the 7th day of IVF. Percutaneous needle biopsy of the vastus lateralis muscle permitted calculation of transmembrane electrolyte distribution from the Nernst equation, using the measured E(m) and the chloride space method. Hospitalization with intake of a defined-formula enteral diet for 3 days resulted in depolarization (P < 0.05) of resting E(m) (-75.3 ± 1.6 mV) compared with normal (-79.8 ± 0.9 mV). Despite 10 days of subsequent IVF, further depolarization (P < 0.05) of resting E(m) (-71.2 ± 1.2 mV) was observed. In the dual presence of IVF and exogenous epinephrine infusion, there was an increase (P < 0.05) in intracellular potassium concentration and repolarization of resting E(m) (-80.6 ± 0.8 mV) to normal levels. These data indicate that hormonal background and substrate availability contribute to the in vivo modulation of cellular membrane function in human skeletal muscle, possibly through facilitation of sodium-dependent amino acid transport across the cell membrane.