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Effects of vagal stimulation and applied acetylcholine on the arrested sinus venosus of the toad.
Author(s) -
Bywater R A,
Campbell G D,
Edwards F R,
Hirst G D
Publication year - 1990
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1990.sp018089
Subject(s) - acetylcholine , hyperpolarization (physics) , stimulation , medicine , endocrinology , sinus venosus , chemistry , membrane potential , biophysics , biology , biochemistry , organic chemistry , nuclear magnetic resonance spectroscopy
1. The effects of vagal stimulation and applied acetylcholine were compared on sinus venosus preparations of the toad, Bufo marinus, in which beating had been inhibited by adding the organic calcium antagonist nifedipine. 2. Bath‐applied acetylcholine and vagal stimulation each caused membrane hyperpolarizations which were abolished by hyoscine. 3. Whereas the hyperpolarization that accompanied vagal stimulation was largely unaffected by barium ions, that produced by bath‐applied acetylcholine was almost abolished. 4. Caesium ions also prevented the hyperpolarization produced by bath‐applied acetylcholine but potentiated the responses to vagal stimulation. 5. The membrane resistance of arrested sinus venosus cells was found to be higher during vagal stimulation than in the absence of stimulation. In contrast when a similar hyperpolarization was produced by adding acetylcholine, the membrane resistance was found to be lower than in control solution. 6. The results are discussed in relation to the idea that neuronally released acetylcholine causes membrane hyperpolarization by suppressing inward current flow and applied acetylcholine acts to increase outward current flow.