Force and membrane potential in acetylcholine and potassium contractures of denervated mouse muscles
Lorković, H.
Pflugers Archiv European Journal of Physiology 404(1): 50-55
1985
ISSN/ISBN: 0031-6768 PMID: 4011399 Document Number: 251856
Depolarization and contracture force (P) provoked by acetylcholine (ACh) and by K+ were studied in bundles dissected from mouse soleus muscles that were denervated for 4-7 days. Cl-free solutions were used. The muscle fibers were depolarized by solutions containing 150 mM K or 10 .mu.M ACh to nearly 0 in mV resulting in maximum P (Pmax). Threshold P was produced when the membrane was depolarized to more than .apprx. -60 mV by both agents. [K] produced 50% Pmax, causing the membrane to depolarize to -42 mV, whereas a potential more positive than -20 mV was required for 50% Pmax to be produced when ACh was used. The rate of depolarization was always higher for ACh than for K. Pretreatment by 0.05 .mu.M ACh (about threshold for P) did not affect the P - [K] relation appreciably showing that ACh did not stabilize the membrane. Nearly equal P was provoked by successive applications of just suprathreshold agent concentrations when the order of application was ACh .fwdarw. K but not with the reverse order. Hypertonicity (by addition of 300 mM sucrose to all solutions) caused PACh to decrease and PK to increase. Evidently, the ACh receptors are located in the surface membrane of the muscle fibers, not in the T-system membranes.