Influence of a period of inactivity on the duration of post-rest action potentials of the mammalian working ventricular myocardium in correlation to the preceding stimulation frequency.
Experiments were carried out on the working right ventricular myocardium of adult cats, guinea-pigs and rabbits. Membrane voltage was recorded by the glass microelectrode technique and the preparations were stimulated with frequencies of 5, 1 and 0.2 Hz. After a steady state had been reached, a pause (TP) lasting 10-600 s was interpolated. The influence of TP on the duration (D) of post-rest action potentials (AP) was studied; the effect of the pause was measured at electric zero level (D0) and at further repolarization levels (-20, -40 and -60 mV, given here as D-20, D-40 and D-60). At 1 and 0.2 Hz frequency, the cat myocardium displayed lengthening of the AP proportional to the duration of the pause; at 5 Hz frequency, D0 reacted by lengthening up to TP = 120 s and to further pauses by slight shortening. D-60, at all frequencies, lengthened throughout the whole of the given TP range. The rabbit myocardium, at all the given frequencies, reacted up to TP = 60-120 s by marked shortening of post-rest AP at all repolarization levels; with longer pauses the AP lengthened. At 5 Hz frequency the guinea-pig myocardium reacted similarly to the cat myocardium; at the lower stimulation frequencies, the pause-induced changes in the post-rest AP were less strongly expressed. In all the given types of myocardium, the most pronounced post-rest AP reactions were those at electric zero level (the plateau phase of the AP); towards more negative repolarization values and with lower pre-pause stimulation frequencies they were less strongly expressed.(ABSTRACT TRUNCATED AT 250 WORDS)
D000200:Action Potentials; D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D008297:Male; D011817:Rabbits; D013045:Species Specificity; D013997:Time Factors; D016276:Ventricular Function