Abstract
It has been possible to study quantitatively the induction of automaticity in isolated quiescent or electrically-driven cat papillary muscle preparation. Epinephrine and norepinephrine were found to be equipotent, while isoproterenol was 7 times more potent than the above. Methoxamine had no effect.
The threshold for induction of automaticity by epinephrine is increased by raising the potassium concentration of the bath fluid or by prior treatment with dichloroisoproterenol.
Small concentrations of chloroform in the medium cause a slight decrease in threshold in most muscles. Phenoxybenzamine has the same effect.
Footnotes
- Received December 27, 1960.
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