title: Direct measurements of SR free Ca reveal the mechanism underlying the transient effects of RyR potentiation under physiological conditions.
abstract: OBJECTIVE
  Most of the calcium that activates contraction is released from the sarcoplasmic reticulum (SR) through the ryanodine receptor (RyR). It is controversial whether activators of the RyR produce a maintained increase in the amplitude of the systolic Ca transient. We therefore aimed to examine the effects of activation of the RyR in large animals under conditions designed to be as physiological as possible while simultaneously measuring SR and cytoplasmic Ca.
  
  
  RESULTS
  Experiments were performed on ventricular myocytes from canine and ovine hearts. Cytoplasmic Ca was measured with fluo-3 and SR Ca with mag-fura-2. Application of caffeine resulted in a brief increase in the amplitude of the systolic Ca transient accompanied by an increase of action potential duration. These effects disappeared with a rate constant of ∼3 s(-1). Similar effects were seen in cells taken from sheep in which heart failure had been induced by rapid pacing. The decrease of Ca transient amplitude was accompanied by a decrease of SR Ca content. During this phase, the maximum (end-diastolic) SR Ca content fell while the minimum systolic increased.
  
  
  CONCLUSIONS
  This study shows that, under conditions designed to be as physiological as possible, potentiation of RyR opening has no maintained effect on the systolic Ca transient. This result makes it unlikely that potentiation of the RyR has a maintained role in positive inotropy.
authors.affiliation: Unit of Cardiac Physiology, Institute of Cardiovascular Science, Manchester Academic Health Science Centre, 3.18 Core Technology Facility, 46 Grafton Street, Manchester M13 9NT, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Greensmith
authors.affiliation: Unit of Cardiac Physiology, Institute of Cardiovascular Science, Manchester Academic Health Science Centre, 3.18 Core Technology Facility, 46 Grafton Street, Manchester M13 9NT, UK.
authors.forename: Gina L J
authors.initials: GL
authors.lastname: Galli
authors.affiliation: Unit of Cardiac Physiology, Institute of Cardiovascular Science, Manchester Academic Health Science Centre, 3.18 Core Technology Facility, 46 Grafton Street, Manchester M13 9NT, UK.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Trafford
authors.affiliation: Unit of Cardiac Physiology, Institute of Cardiovascular Science, Manchester Academic Health Science Centre, 3.18 Core Technology Facility, 46 Grafton Street, Manchester M13 9NT, UK eisner@man.ac.uk.
authors.forename: David A
authors.initials: DA
authors.lastname: Eisner
mesh_terms: D000814:Aniline Compounds / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D004285:Dogs; D016257:Fura-2 / Q000031:analogs & derivatives / Q000032:analysis; D006321:Heart / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012756:Sheep; D014966:Xanthenes / Q000032:analysis
chemical_list: D000814:Aniline Compounds; D019837:Ryanodine Receptor Calcium Release Channel; D014966:Xanthenes; C058776:2-(2-(5-carboxy)oxazole)-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic acid; C059715:Fluo-3; D002118:Calcium; D016257:Fura-2
keywords: Calcium; Ryanodine receptor; Sarcoplasmic reticulum