title: Role of non-quantal acetylcholine release in surplus polarization of mouse diaphragm fibres at the endplate zone.
abstract: 1. In mouse diaphragm, with intact cholinesterase (ChE), the mean value of the resting membrane potential was significantly higher (-84.8 +/- 0.3 mV; mean +/- S.E.M.) at the endplate zone than in the extrajunctional area of the muscle fibres (-82.5 +/- 0.3 mV) at 22 degrees C. 2. This hyperpolarization of about 2-3 mV at the endplate zone was abolished within 5 min by 1 x 10(-6) M ouabain, indicating that it might be caused by an electrogenic Na(+)-K+ pump. (+)-Tubocurarine (TC; 1 x 10(-5) M) had no effect on this hyperpolarization after bath application for 10-20 min. 3. Short-term denervation (4 h), a slight increase of Mg2+ in the bath of from 1 to 4 mM and application of a Ca(2+)-free solution for 60 min also led to the disappearance of the surplus polarization. All of these factors are known to eliminate TC-induced hyperpolarization in anti-ChE-treated muscles (H-effect), which is considered to be a correlate of non-quantal acetylcholine (ACh) leakage. 4. The time courses of the decline of the H-effect and surplus polarization after denervation were identical. 5. In short-term denervated muscles with intact ChE, the surplus polarization was restored by 5 x 10(-8) M ACh, which simulates the H-effect in anti-ChE-treated muscles. The presence of 1 x 10(-6) M ouabain either prevented or abolished the effect of the bath-applied ACh.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Kazan Medical Institute, Tatarstan, Russia.
authors.forename: E E
authors.initials: EE
authors.lastname: Nikolsky
authors.forename: H
authors.initials: H
authors.lastname: Zemková
authors.forename: V A
authors.initials: VA
authors.lastname: Voronin
authors.forename: F
authors.initials: F
authors.lastname: Vyskocil
mesh_terms: D000109:Acetylcholine / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D002802:Cholinesterases / Q000378:metabolism; D003964:Diaphragm / Q000294:innervation / Q000378:metabolism* / Q000502:physiology; D004594:Electrophysiology; D005260:Female; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D009045:Motor Endplate / Q000378:metabolism*; D009121:Muscle Denervation; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology; D013997:Time Factors; D014403:Tubocurarine / Q000494:pharmacology
chemical_list: D002800:Cholinesterase Inhibitors; D002802:Cholinesterases; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D000109:Acetylcholine; D002118:Calcium; D014403:Tubocurarine