Excitation-contraction coupling of cultured human skeletal muscle cells and the relation between basal cytosolic Ca2+ and excitability.
Cultured human skeletal muscle cells are frequently used as a model to study muscle pathology, in which Ca2+ homeostasis might be affected. However, their excitation-contraction (E-C) coupling has been poorly investigated. In order to elucidate E-C coupling of cultured muscle cells, we activated the acetylcholine receptors, voltage-dependent Na+ channels, dihydropyridine receptors or ryanodine receptors both in the presence and absence of external Ca2+, as well as after specific inhibition, and measured the effects on the cytosolic Ca2+ concentration ([Ca2+]i) using Fura-2. Furthermore, we examined the excitability of these cells during iterative high (125 mM) K+ stimulation with various repolarisation intervals. The resting [Ca2+]i in muscle cells of controls is about 130 nM. Acetylcholine, veratridine, high K+ and caffeine elicit dose-dependent Ca2+ transients, which are independent of extracellular Ca2+ and can be inhibited by alpha-bungarotoxin, tetrodotoxin, nifedipine or ryanodine. During repetitive K+ stimulation, the excitability of the muscle cells depends on the repolarisation interval between successive stimulations. Upon shortening the repolarisation time the Ca2+ transients become smaller and slower. Thereby, the basal [Ca2+]i rises, the Ca2+ response amplitude declines and both the half-increase and half-decay time increase. However, if the basal [Ca2+]i equals the resting [Ca2+]i the initial Ca2+ response can be recovered. The intracellular pH of 7.23, measured by BCECF, is unaffected by repeated K+ stimulation, whatever the repolarisation interval was. In conclusion, cultured human skeletal muscle cells possess a 'skeletal muscle type' of E-C coupling and their excitability at iterative stimulation is set by their basal [Ca2+]i.
Benders
A A
AA
Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands.
Oosterhof
A
A
Wevers
R A
RA
Veerkamp
J H
JH
D000109:Acetylcholine / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002138:Calibration; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology
D002110:Caffeine; D014701:Veratridine; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium