[Dynamics of rhythm-dependent potentiation in the guinea pig heart]

In strip preparations from the right ventricle of the guinea pig heart, potentiation phenomena due to varied pacing rate (frequency potentiation FP) or paired stimulation (paired pulse potentiation PPP) are studied with respect to contractile strength and dynamics. Heart rate or interstimulus interval of paired stimulation were modulated both stepwise and sinusoidally. Steady state characteristics of FP as well as PPP prove to be linear in a broad range. FP is enhanced by increasing rate, whereas PPP is diminished by increasing interval. Paired stimulation is always more effective than single stimulation at double rate. Effects upon action potential are negligible. The response of PPP to interval steps are first order transients, whereas rate steps produce on/off response of FP, opposite to step direction, with subsequent staircase. Frequency response characteristics of FP and PPP yield in first order transfer functions: for PPP with dead time, and for FP with negative derivative action. After substitution of Ca++ by Sr++ ions, the negative derivative term of FP disappears, whereas positive staircase remains. By means of a compartment hypothesis of electromechanical coupling in the mammalian myocardium the mode of action of the potentiation phenomena and their differences are interpreted, and the obtained dynamic parameters are attributed to presumably underlying Ca transport processes within the cell.