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The effect of noradrenaline on the end‐plate potential in twitch fibres of the frog
Author(s) -
Jenkinson D. H.,
Stamenović B. A.,
Whitaker Beatrice D. L.
Publication year - 1968
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.1968.sp008486
Subject(s) - acetylcholine , chemistry , endocrinology , medicine , iontophoresis , biophysics , biology , neuroscience
1. The action of noradrenaline in increasing the amplitude of the end‐plate potential (e.p.p.) has been studied in magnesium‐blocked frog skeletal muscle. 2. Noradrenaline (10 −5 M ) increased the e.p.p. by about 20% without causing any comparable change in the amplitude of the miniature end‐plate potentials (m.e.p.p.s). It was concluded that noradrenaline acts by potentiating the release of acetylcholine by the nerve impulse, rather than by increasing the sensitivity of the end‐plate. 3. In support of this, it was found that the increase in e.p.p. amplitude was associated with a reduction in the variability of successive e.p.p.s, as is to be expected if the quantal content of the e.p.p. became larger. Further, noradrenaline was without effect on the response to iontophoretically‐applied acetylcholine, although it potentiated depolarizations elicited by acetylcholine applied for much longer periods in the bathing fluid. 4. Noradrenaline increased the frequency of occurrence of m.e.p.p.s, and unusually large m.e.p.p.s. were occasionally observed.