The role of extracellular calcium in the contractions produced by acetylcholine in chronically denervated muscle.
1 Acetylcholine-induced contractions of the isolated chronically denervated soleus muscle of the mouse consist of two phases, but both phases are equivalent to the contracture phase seen in vivo.2 Low [Ca(2+)](0) (0.5-1.5 mM) augmented peak tension, as well as the rate of relaxation, of the first phase, but inhibited the second phase. Ethyleneglycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) or La(3+) (2 mM) also inhibited the second phase, but not the first.3 It was concluded that the first phase requires Ca(2+) release from the sarcoplasmic reticulum, and is terminated by inactivation of the contractile process. The second phase is caused by the entry of activator Ca(2+) from the extracellular space.4 Increasing [Ca(2+)](o) to 5 or 10 mM after the addition of acetylcholine caused a contraction, starting after a delay of about 50 seconds. EGTA or La(3+) added during the second phase of the acetylcholine contraction caused relaxation after a much shorter lag time.5 It is concluded that most of the Ca(2+) entering from the extracellular fluid is taken up by the sarcoplasmic reticulum.6 The acetylcholine second phase was augmented in low (25 mM) [Na(+)](0). It is concluded that Na(+) and Ca(2+) compete for the acetylcholine controlled ionic channels.7 Isolated chronically denervated diaphragm muscles were less sensitive to acetylcholine and the contraction usually consisted of a first phase only.8 It is concluded that sequestration of Ca(2+) entering from the extracellular fluid is more complete in the diaphragm.
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005110:Extracellular Space / Q000032:analysis; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects*; D009121:Muscle Denervation; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D002110:Caffeine; D004533:Egtazic Acid; D011189:Potassium Chloride; D007811:Lanthanum; D000109:Acetylcholine; D002118:Calcium