Na+-K+-ATPase is not involved in the warming-up phenomenon in generalized myotonia.
The initial temporary weakness that occurs in autosomal-recessive generalized myotonia diminishes with repetitive contractions. Physiological understanding of this phenomenon is incomplete. The underlying hypothesis of our study was that the "warming-up" phenomenon relates to the exercise-related activation of Na(+)-K(+)-ATPase. Three patients performed isometric exercise of the brachioradialis muscle on two separate days. Randomly, on one of these days the contraction was preceded by a 30-min infusion of the Na(+)-K(+)-ATPase inhibitor ouabain into the brachial artery of the exercising arm (0.4 mug.min(-1).dl(-1)). Force was measured simultaneously with electrical muscle activity using high-density surface electromyography (HD-sEMG). A transient rapid decline in force occurred after initiation of exercise, accompanied by electrophysiological changes indicating sarcolemmal conduction block. Ouabain infusion did not affect the recovery from transient paresis or the accompanying electromyographic changes, indicating that the warming-up phenomenon in generalized myotonia is not mediated by Na(+)-K(+)-ATPase.
Van Beekvelt
Mireille C P
MC
Department of Clinical Neurophysiology, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
Drost
Gea
G
Rongen
Gerard
G
Stegeman
Dick F
DF
Van Engelen
Baziel G M
BG
Zwarts
Machiel J
MJ
D000328:Adult; D004576:Electromyography; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009224:Myotonia Congenita / Q000503:physiopathology*; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D010291:Paresis / Q000503:physiopathology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000502:physiology*
D004791:Enzyme Inhibitors; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase