Influence of ryanodine on the mechanical restitution and on the post-extrasystolic potentiation of the guinea-pig ventricular myocardium.
This paper records the results of an investigation into potentiation and staircase phenomena in rightventricular guinea-pig papillary muscles with particular reference to the sarcoplasmic Ca(2+)-channel. As a tool to isolate the second ('late', 'tonic') component of isoproterenol-induced biphasic contractions ryanodine was used. On the evidence at present available the monophasic ryanodine-resistant component of the twitch represents that portion of the activator calcium which reaches the troponin C directly, that is, not taking the roundabout way through the intracellular storage structures. In order to avoid functional instabilities of the isolated muscle preparation a short-time double rest stimulation programme was used which combines a number of different tests and gives information on (1) the post-rest potentiation, (2) the post-extrasystolic potentiation, (3) the mechanical post-rest recovery, (4) the interval-strength relationship, and (5) the mechanical restitution. The results of the present work show that under the influence of ryanodine (1) the Bowditch staircase, a typical feature of normodynamic mammalian ventricular preparations as well as of hypodynamic frog heart preparations, does not exist, (2) the post-extrasystolic potentiation disappears, (3) the curve reflecting the mechanical restitution, under normal in vitro conditions a monotonically increasing function, becomes biphasic within the relative refractory period, (4) the conspicuous depression of the isometric post-rest contraction for long lasting pauses interrupting the regular pacing rhythm, a typical feature of isolated guinea-pig ventricular tissue, is clearly diminished, and (5) the characteristic curve, reflecting the potentiation of the post-extrasystolic post-rest contraction as a function of the delay time preceding the extrastimulus, becomes displaced to the premature interstimulus interval. The concept of an 'extended 2-calcium-store model' is supported by this work.
Oblonczek
G
G
Julius-Bernstein-Institut für Physiologie, Martin-Luther-Universität Halle-Wittenberg, Halle/Saale, Germany.
Szymanski
G
G
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002316:Cardiotonic Agents / Q000494:pharmacology*; D004594:Electrophysiology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D010210:Papillary Muscles / Q000187:drug effects* / Q000502:physiology; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D002316:Cardiotonic Agents; D012433:Ryanodine; D002118:Calcium