The Relation Between Excitability and Contractility in the Isolated Rabbit Atrium

Abstract

Diastolic excitability and isometric contraction force were measured in the isolated left atrium of the rabbit. Within limits an increase in stimulation frequency resulted in increased contraction force with no essential change in excitability. After a peak response was attained a further increase in frequency resulted in a decrease in force and also in excitability. Outside the refractory period there was no relation between excitability and tension developed at various frequencies. in strength-interval determination diastolic excitability was higher in the 960 msec. cycle and diastolic contractility was greater in the 630 msec. cycle. the pattern of recovery of excitability was similar for both cycles and seemed to be governed by the duration of the refractory period. A contractile response was recorded throughout a given cycle, but the rate of recovery of contractility was faster in the shorter cycle. Diastolic contraction force was obtained only at the end of the cycle. It is concluded that in the isolated rabbit atrium there is no relation between recovery of excitability and recovery of contractility.