Muscle function in a patient with Brody's disease.
Adductor pollicis muscle function of a 21-year-old man with genetically confirmed Brody's disease (sarcoplasmic reticulum [SR] -Ca2+ATPase deficiency) was investigated to study the possible effects of reduced SR-Ca2+ATPase activity on muscle relaxation and force production. Following maximal electrical activation of the ulnar nerve, tetanic muscle half-relaxation time was greater in the patient (246 +/- 10 ms) than control subjects (97 +/- 4 ms, n = 8). During repetitive activation, there was a similar decline in maximal shortening velocity in the patient and controls, indicating a comparable reduction in cross-bridge cycling rate. The finding that the slowing of relaxation was greater in the patient (329 ms versus 138 +/- 20 ms) suggests that there was a further reduction of SR-Ca2+ATPase activity in the patient's muscle during fatigue. Following a voluntary contraction, involuntary activity of the antagonist muscles facilitated force decline and masked the impaired relaxation in the patient. This antagonist-induced relaxation indicates that it might be difficult to establish impaired muscle relaxation with voluntary contractions.
De Ruiter
C J
CJ
Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands.
Wevers
R A
RA
Van Engelen
B G
BG
Verdijk
P W
PW
De Haan
A
A
D000328:Adult; D000252:Calcium-Transporting ATPases / Q000172:deficiency / Q000235:genetics*; D004576:Electromyography; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009135:Muscular Diseases / Q000201:enzymology / Q000235:genetics*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
D000252:Calcium-Transporting ATPases