[Energy providing metabolism of muscles in periodic paralysis]

Hypokalemic periodic paralysis: in vitro investigation of muscle fiber membrane parameters

To study the mechanism of attacks in familial hypokalemic paralysis, we recorded resting membrane potentials, action potentials, current-voltage relationships, and isometric forces in intercostal muscle fibers from three patients. In normal extracellular medium, the resting potential was reduced, but membrane conductance was not different from control. Excitability was reduced and the action potentials had no overshoot. On exposure to a 1-mM potassium solution, with or without insulin, the cells depolarized to about -50 mV, and became inexcitable. Over the tested membrane potential range from -120 to -40 mV, the slope conductance in the 1-mM potassium solution was not different from that of control fibers in a 1-mM potassium solution. In particular, the potassium component conductance was not reduced. Depolarized fibers could not be completely repolarized by returning to a 3.5-mM potassium solution. An experimentally induced transient shift of the chloride equilibrium potential to a highly negative value caused stable repolarization. Paralysis could also be induced by replacement of extracellular chloride with an impermanent anion, a treatment which causes myotonia in healthy fibers. It was concluded that the basic defects are a reduced excitability and an increased sodium conductance, and that these defects are aggravated on reduction of the extracellular potassium concentration.

M. Quadriceps femoris of man, a muscle with an unusual enzyme activity pattern of energy supplying metabolism in mammals

1. The following enzyme activities were estimated in needle-biopsy samples of the lateral part of the human quadriceps femoris muscle: triosephosphate dehydrogenase (TPDH), lactate dehydrogenase (LDH), NAD : glycerol-3-phosphate dehydrogenase (GPDH), hexokinase (HK), NAD: malate dehydrogenase (MDH), citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase. 2. Although the enzyme activities in muscles of women were lesser than in those of men, no difference was found in the calculated enzyme activity ratios. There is thus no sex-dependent metabolic type-differentiation in this muscle. 3. The human quadriceps femoris is a low-activity muscle, in comparison with muscles of homoiotherm laboratory animals. The enzyme activity ratio of TPDH to CS, characterizing the glycolytic pyruvate formation to aerobic oxidative capacities, shows this muscle to be of an intermediate type in this respect, similarly as the extensor digitorum longus of the rat. The relatively very high capacity of glucose phosphorylation (HK), the high aerobic regeneration of cytoplasmic dehydrogenated NAD (GPDH) and the very low anaerobic regeneration (LDH), show the unusually high proportion of carbohydrates (glucose) which can be broken down aerobically.