Comparison of subsarcolemmal and bulk calcium concentration during spontaneous calcium release in rat ventricular myocytes

Andrew Trafford, M. E. Diaz, Stephen O'Neill, D. A. Eisner

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    1. The aim of these experiments was to compare the time course of changes in intracellular Ca2+ concentration ([Ca2+](i)) measured in the bulk cytoplasm with those estimated to occur near the sarcolemma. Sarcolemmal Na+-Ca2+ exchange current and [Ca2+](i) were measured in single, voltage-clamped ventricular myocytes. 2. Spontaneous Ca2+ release from the sarcoplasmic reticulum (SR) resulted in a transient inward current. This current developed and decayed more quickly than the accompanying changes in [Ca2+](i) (measured with indo-1) resulting in a hysteresis between [Ca2+](i) and current. A similar hysteresis was also observed if [Ca2+](i) was elevated with caffeine and was removed if the current was low pass filtered with a time constant of 132 ms. Digital video imaging (using fluo-3 or calcium green-1. to measure [Ca2+](i)) allowed measurement of [Ca2+]1 at all points in the cell during the wave of spontaneous Ca2+ release. The hysteresis between [Ca2+]1 and current remained, even after allowing for the spatial and temporal properties of this wave. 4. The hysteresis can be accounted for if there is a barrier to diffusion of Ca2+ ions separating the bulk cytoplasm from the space under the sarcolemma (into which Ca2+ is released from the sarcoplasmic reticulum). The calculated subsarcolemmal [Ca2+] rises and falls more quickly (and reaches a higher peak) than does the bulk [Ca2+]. The delay introduced by this barrier is equivalent to a time constant of 133 ms. 5. The subsarcolemmal space described in this paper may be equivalent to the 'fuzzy space' previously suggested to be important in controlling SR Ca2+ release.
    Original languageEnglish
    Pages (from-to)577-586
    Number of pages9
    JournalJournal of Physiology
    Issue number3
    Publication statusPublished - 1995


    • Animals
    • physiology: Biological Transport
    • metabolism: Calcium
    • physiology: Cell Compartmentation
    • Comparative Study
    • Fluorescent Dyes
    • cytology: Heart Ventricles
    • Indoles
    • cytology: Myocardium
    • Patch-Clamp Techniques
    • Rats
    • Research Support, Non-U.S. Gov't
    • metabolism: Sarcolemma


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