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Comparison of subsarcolemmal and bulk calcium concentration during spontaneous calcium release in rat ventricular myocytes.
Author(s) -
Trafford A W,
Díaz M E,
O'Neill S C,
Eisner D A
Publication year - 1995
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1995.sp020991
Subject(s) - sarcolemma , endoplasmic reticulum , calcium , chemistry , biophysics , cytoplasm , myocyte , time constant , analytical chemistry (journal) , endocrinology , biology , biochemistry , chromatography , membrane , organic chemistry , engineering , electrical engineering
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. 3. Digital video imaging (using fluo‐3 or calcium green‐1 to measure [Ca2+]i) allowed measurement of [Ca2+]i at all points in the cell during the wave of spontaneous Ca2+ release. The hysteresis between [Ca2+]i 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.