Perchlorate potentiation of excitation-contraction coupling in mammalian skeletal muscles.
The action of perchlorate (ClO4-), an agonist of the voltage sensor in excitation-contraction (EC) coupling, has been examined using bundles of intact muscle cells, isolated membrane vesicles [sarcoplasmic reticulum (SR) and transverse tubule (TT)], and cultured myotubes. The effect of ClO4- on mechanical parameters was investigated in isolated murine limb muscles. The presence of ClO4- (5 or 10 mM) greatly increased twitch tension ( > 250%), slightly enhanced tetanic tension, and increased K contracture tension. K contracture thresholds of extensor digitorum longus (EDL, 40 mM K+) and soleus (30 mM K+) muscles were not altered by ClO4-. However, in whole cell patch clamp studies of mouse myotubes, contractile activation was shifted by approximately -10 mV by 10 mM ClO4-. To further define the site of alteration of EC coupling by ClO4-, studies were conducted with isolated porcine SR and TT vesicles and with cultured mouse myotubes. The rate constant of Ca-induced 45Ca release from SR vesicles was significantly increased by ClO4-. However, neither the affinity nor level of [3H]PN200-110 binding to TT vesicles was significantly affected by ClO4- concentrations that increased twitch tension. Furthermore, slow plasmalemmal Ca currents of myotubes recorded in the whole cell patch-clamp mode were enhanced by 10 mM ClO4-, and the current-voltage relationship was shifted approximately -7mV. Thus, in enhancing EC coupling in mammalian muscle, ClO4- may act at multiple sites including the SR Ca release channel and the TT Ca channel-voltage sensor.
Gallant
E M
EM
Graduate Program in Veterinary Biology, University of Minnesota, St. Paul 55108.
Taus
N S
NS
Fletcher
T F
TF
Lentz
L R
LR
Louis
C F
CF
Mickelson
J R
JR
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004095:Dihydropyridines / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D010472:Perchlorates / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology
D015220:Calcium Channels; D004095:Dihydropyridines; D010472:Perchlorates; D011188:Potassium