Premium
RESTING AND STIMULATION‐INDUCED EFFLUX OF TRITIUM FROM GUINEA‐PIG ATRIA INCUBATED WITH 3H‐NORADRENALINE
Author(s) -
McCulloch M. W.,
Rand M. J.,
Story D. F.
Publication year - 1974
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1974.tb00550.x
Subject(s) - efflux , stimulation , medicine , endocrinology , tetrodotoxin , chemistry , tyramine , biology , biochemistry
SUMMARY 1. After incubation of guinea‐pig atria with 3 H‐(—)‐noradrenaline, the spontaneous efflux of radioactivity showed two components, an initial rapid efflux with a half life of about 5 min and a slower efflux with a half life greater than 40 min. 2. Field stimulation produced an increase in efflux of radioactivity and the force of atrial contractions. 3. There was a linear relationship between the spontaneous efflux of radioactivity and the total efflux during periods of stimulation. This was maintained for three periods of stimulation at 30 min intervals. The increase in efflux during stimulation over that in the corresponding resting periods was termed the stimulation‐induced efflux. 4. Tetrodotoxin (1.56 μM) markedly reduced the stimulation‐induced efflux and the increase in contractile force in response to stimulation, indicating that these effects were due to excitation of intramural adrenergic nerves. Tetrodotoxin also decreased resting efflux. 5. Cocaine (0.1–3 μM) reduced the resting efflux but increased resting contractile force; increases in both stimulation‐induced efflux and positive inotropic response to stimulation were produced. A higher concentration (300 μM) increased resting efflux, decreased stimulation‐induced efflux, and decreased contractile force in resting and stimulation periods. 6. Guanethidine in a low concentration (0.1 μM) increased stimulation‐induced efflux and the positive inotropic response to stimulation. A higher concentration (10 μM) markedly increased resting efflux and the resting contractile force; the positive inotropic response to stimulation was only slightly reduced but the'stimulation‐induced efflux was greatly reduced. 7. Tyramine (100 μM) increased the resting efflux and initially increased resting contractile force. Tyramine also increased stimulation‐induced efflux; however, it depressed the positive inotropic response to stimulation. These effects of tyramine were much less marked in the presence of cocaine (100 μM). 8. Normetanephrine (10 μM) counteracted the effects of cocaine (1 μM) on effluxes and contractile force, but had little or no effect on its own.