title: Comparison of subsarcolemmal and bulk calcium concentration during spontaneous calcium release in rat ventricular myocytes.
abstract: 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.
authors.affiliation: Department of Veterinary Preclinical Sciences, University of Liverpool, UK.
authors.forename: A W
authors.initials: AW
authors.lastname: Trafford
authors.forename: M E
authors.initials: ME
authors.lastname: Díaz
authors.forename: S C
authors.initials: SC
authors.lastname: O'Neill
authors.forename: D A
authors.initials: DA
authors.lastname: Eisner
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation / Q000502:physiology; D005456:Fluorescent Dyes; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D007211:Indoles; D009206:Myocardium / Q000166:cytology*; D018408:Patch-Clamp Techniques; D051381:Rats; D012508:Sarcolemma / Q000378:metabolism*
chemical_list: D005456:Fluorescent Dyes; D007211:Indoles; C048960:indo-1; D002118:Calcium