Post-rest contractions of amphibian cardiac muscle.
Post-rest potentiated contractions have been reported to be more dependent on Ca2+ stored in intracellular sites than on transmembrane Ca2+ influx. The phenomenon was examined using toad ventricular strips contracting isometrically and superfused with Ringer solution. Toad ventricular strips did not present post-rest potentiation, a fact that may be explained by the reduced volume of the sarcoplasmic reticulum in the amphibian myocardium. Potentiated post-rest contractions were obtained after calcium influx blockade with 10 microM verapamil or 2 mM Mn2+ and the slow reduction of extracellular Ca2+ concentration obtained by slowly exchanging the bath fluid was accompanied by a progressive decrease of both steady-state and post-rest contractions. These data confirm the observations made on other species regarding the post-rest potentiation phenomenon and support the suggestion of the dependence of post-rest potentiation on activator calcium liberated from intracellular stores.
Leite
C M
CM
Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, Brasil.
Vassallo
D V
DV
Mill
J G
JG
D000818:Animals; D002024:Bufo marinus; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides; D005110:Extracellular Space / Q000502:physiology*; D008345:Manganese / Q000494:pharmacology; D017895:Manganese Compounds; D008564:Membrane Potentials / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology*; D014700:Verapamil / Q000494:pharmacology
D002712:Chlorides; D017895:Manganese Compounds; D008345:Manganese; D014700:Verapamil; C025340:manganese chloride; D002118:Calcium