Ouabain induces acetylcholine release from pure cholinergic synaptosomes independently of extracellular calcium concentration.
We have studied the correlation between [3H]ouabain binding sites, (Na+ + K+)ATPase (EC 3.6.1.3) activity and acetylcholine (ACh) release in different subcellular fractions of Torpedo marmorata electric organ (homogenate, synaptosomes, presynaptic plasma membranes). Presynaptic plasma membranes contained the greater number of [3H]ouabain binding sites, in good agreement with the high (Na+ + K+)ATPase activity found in this fraction. Blockade of this enzymatic activity by ouabain dose-dependently induced ACh release from pure cholinergic synaptosomes, either in the presence or absence of extracellular calcium ions. We suggest that one of the mechanisms involved in the ouabain-induced ACh release in the absence of Ca2+o may be an increase in Na+i that could (a) evoke Ca2+ release from internal stores and (b) inhibit ATP-dependent Ca2+ uptake by synaptic vesicles.
Blasi
J M
JM
Departament de Biologia Cellular, i Anatomia Patològica, Facultat de Medicina, Hospital de Bellvitge, Universitat de Barcelona, Spain.
Ceña
V
V
González-García
C
C
Marsal
J
J
Solsona
C
C
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002799:Cholinergic Fibers / Q000378:metabolism*; D004557:Electric Organ; D066298:In Vitro Techniques; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology*; D011869:Radioligand Assay; D012964:Sodium / Q000378:metabolism; D013574:Synaptosomes / Q000378:metabolism*; D014101:Torpedo
D010042:Ouabain; D012964:Sodium; D000109:Acetylcholine; D002118:Calcium