AJP - Cell Physiology, Vol 265, Issue 6 C1703-C1710, Copyright © 1993 by American Physiological Society

ARTICLES

Beat-to-beat measurements of [Ca2+]i and force in ferret cardiac muscle after chemical loading of aequorin

F. Urthaler, A. A. Walker, R. C. Reeves and L. L. Hefner
Department of Medicine, University of Alabama at Birmingham 35294.

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.

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