RESTING MEMBRANE-POTENTIAL OF SKELETAL-MUSCLE CALCULATED FROM PLASMA AND MUSCLE ELECTROLYTE AND WATER CONTENTS

1. A method is described that enables the calculation of resting membr ane potential from the electrolyte and water contents in blood plasma and in a sample of human muscle tissue obtained by the percutaneous ne edle-biopsy technique, In this calculation, the previously described e quations for calculating resting membrane potential via the intra- and extra-cellular distribution of chloride were combined with the equati on utilizing potassium distribution over the cell membrane, 2. The met hod of calculation was applied to 60 healthy subjects divided into thr ee groups aged 19-40, 41-60 and 61-85 years, The calculated resting me mbrane potential in the subjects as a whole was -88.4 mV (SD 1.35; n = 60), A lower value was observed in the group aged 61-85 years (-87.7 mV, SD 1.0; n = 12) than in the group aged 19-40 years (-88.6 mV; SD 1 .4; n=32). No difference was observed between female and male subjects , 3. The RMP calculated with the present method in 60 healthy subjects was also compared with previously published values in healthy subject s, measured by the Clarke electrode method, and with values calculated from electrolyte and water distribution measured by isotope-dilution techniques, The results obtained in healthy subjects with different te chniques were very similar, Data were analysed from earlier published studies in experimental animals in which resting membrane potential ra nged from -91 to -65 mV, The resting membrane potential calculated fro m electrolytes in plasma and muscle showed a very good agreement with resting membrane potential recorded directly.