[The role of intra- and extracellular calcium sources in the rhythmic inotropic regulation of isometric contractions in the chick embryo myocardium].
Isometric contractions and force-frequency relationships (FFR) were assessed in isolated ventricular preparations of 3- and 4-day chick embryos (EM) and posthatched (PH) chicks. Pacing protocols for the FFR assessment were applied in normal buffer, buffer with 50% and 25% of normal Na+ concentration, and in buffer with ryanodine. PH myocardium showed greater peak force and more prominent FFR than EM. 50% low Na+ superfusion induced positive inotropic effect and increase in the FFR in PH and EM. 25% low Na+ superfusion induced negative inotropic effect and suppressed FFR more prominent in EM. Ryanodine more suppressed FFR in PH myocardium. The observed age-dependent differences substantiate the fact that Na-Ca exchange plays a leading role in the FFR regulation in early embryonic myocardium and sarcoplasmic reticulum plays a leading role in PH myocardium.
Tsyv'ian
P B
PB
Institute of Physiology, Ural Branch of the Russian Acad. Ekaterinburg, Russia.
Rutkevich
S M
SM
Protsenko
Iu L
IuL
Tsyv'ian
E P
EP
Miller
K E
KE
Keller
B B
BB
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D002645:Chickens; D003864:Depression, Chemical; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism; D006321:Heart / Q000196:embryology / Q000502:physiology; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D007537:Isometric Contraction / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism; D010507:Periodicity; D012433:Ryanodine / Q000494:pharmacology; D012964:Sodium / Q000172:deficiency; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
D019831:Sodium-Calcium Exchanger; D012433:Ryanodine; D012964:Sodium; D002118:Calcium