title: Beat-to-beat measurements of [Ca2+]i and force in ferret cardiac muscle after chemical loading of aequorin.
abstract: This communication reports the development of a modified procedure for chemical loading of aequorin in small multicellular cardiac preparations, with special emphasis directed toward the implementation of a new method for computer-controlled low-photon counting and digital processing and analysis of the data to obtain intracellular Ca2+ concentration ([Ca2+]i). In eight ferret right ventricular trabeculae, we measured the mechanical performance and found that, at 1.25 mM extracellular Ca2+ concentration ([Ca2+]o), resting tension, developed tension, and time to peak tension were unchanged by the loading procedure. Estimated resting and peak systolic [Ca2+]i were 299 +/- 65 and 766 +/- 131 nM, respectively. Thirty minutes after raising the [Ca2+]o to 5 mM, there was a robust increase in mechanical performance, with peak systolic [Ca2+]i averaging 1,218 +/- 222 nM. The diastolic [Ca2+]i remained unchanged. In four other trabeculae, exposure to a low-Na(+)-containing superfusate demonstrated a remarkable beat-to-beat correspondence of increases in diastolic [Ca2+]i and resting tensions. The same beat-to-beat concordance was also observed between the rapidly changing amplitudes of peak [Ca2+]i and developed tension. In additional experiments, simultaneous recordings of [Ca2+]i and force transients were obtained during rapid pace pause maneuvers. These studies showed distinct and quantifiable fluctuations of [Ca2+]i in a 1:1 relation to the mechanical record to a frequency of at approximately 300 beats/min. These results demonstrate that beat-to-beat measurements of [Ca2+]i and tension transients can be obtained with good resolution in multicellular cardiac preparations.
authors.affiliation: Department of Medicine, University of Alabama at Birmingham 35294.
authors.forename: F
authors.initials: F
authors.lastname: Urthaler
authors.forename: A A
authors.initials: AA
authors.lastname: Walker
authors.forename: R C
authors.initials: RC
authors.lastname: Reeves
authors.forename: L L
authors.initials: LL
authors.lastname: Hefner
mesh_terms: D000331:Aequorin; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003201:Computers; D003971:Diastole; D004576:Electromyography / Q000295:instrumentation / Q000379:methods; D005289:Ferrets; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D066298:In Vitro Techniques; D008163:Luminescent Measurements; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism; D010210:Papillary Muscles / Q000378:metabolism / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology
chemical_list: D000331:Aequorin; D012964:Sodium; D002118:Calcium