Sodium, Potassium, and Chloride Fluxes in Intercostal Muscle from Normal Goats and Goats with Hereditary Myotonia

Abstract

In isolated bundles of external intercostal muscle from normal goats and goats with hereditary myotonia the following were determined: concentrations and unidirectional fluxes of Na+, K+, and C-, extracellular volume, water content, fiber geometry, and core-conductor constants. No significant difference between the two groups of preparations was found with respect to distribution of fiber size, intracellular concentrations of Na+ or Cl-, fiber water, resting membrane potential, or overshoot of action potential. The intracellular C1-concentration in both groups of preparations was 4 to 7 times that expected if C1-were distributed passively between intracellular and extracellular water. The membrane permeability to K (Ps) calculated from efflux data was (a) at 38°C, 0.365 X 10 -6 cm sec -1 for normal and 0.492 X 10-6 for myotonic muscle, and (b) at 250°C, 0.219 X 10-6 for normal and 0.199 X 10-6 for myotonic muscle. From C1-washout curves of normal muscle usually only three exponential functions could be extracted, but in every experiment with myotonic muscle there was an additional, intermediate component. From these data Pcl could be calculated; it was 0.413 X 10-6 cm sec-1 for myotonic fibers and was > 0.815 X 10-6 cm sec-1 for normal fibers. The resting membrane resistance of myotonic fibers was 4 to 6 times greater than that of normal fibers.

Cable parameters, sodium, potassium, chloride, and water content, and potassium efflux in isolated external intercostal muscle of normal volunteers and patients with myotonia congenita

“…We have compared our human results with similar data we obtained in isolated external intercostal muscle from the goat (1,2). METHODS Normal volunteers.…”

“…We reported abnormalities of cable parameters, ion content, and Cl-permeability in external intercostal muscle isolated from goats with hereditary myotonia (1,2). On extending these observations to man, we realized that cable parameters in isolated human external intercostal muscle have been reported for only seven fibers from two persons (3); ion content after several hours in physiological salt solution has been reported in only one other investigation (4); and no studies of the kinetics of exchange of K+ have been reported for any isolated human muscle.…”

“…Extracellular volume and cell geometry. Extracellular volume was determined by equilibration of preparations of external intercostal muscle with M4C-labeled mannitol9 by methods previously reported (1). Cell dimensions were measured from projected cross sections (magnification 1000) of formalin-fixed, paraffin-embedded preparations (1).…”

“…It is generally recognized that during conventional histological preparation a shrinkage occurs. A correction factor (1.42 for perimeter and 2.02 for area), calculated from Creese (8), has been applied to the measured perimeter and area in calculating cable parameters and ion flux data ( Tables 1, 11, V, and VI); it was applied to data reported by Bryant (2) but not to data reported by Lipicky and Bryant (1).…”

The non-dystrophic myotonias: molecular pathogenesis, diagnosis and treatment

“…In myotonia congenita, the enhanced excitability is due to reduced sarcolemmal chloride conductance and was initially demonstrated in muscles of myotonic goats (Lipicky et al, 1966;Bryant., 1969) and later in humans (Lipicky et al, 1971). Compared with other excitable cells, skeletal muscle has an unusually high chloride conductance, accounting for up to 85% of the resting membrane conductance .…”