Ca2+ sparks triggered by patch depolarization in rat heart cells

Stephen R. Shorofsky, Leighton Izu, Withrow Gil Wier, C. William William Balke

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19 Scopus citations


The goal of this study was to examine the relationship between Ca2+ entry through L-type Ca2+ channels and local [Ca2+](i) transients (Ca2+ sparks) in single rat cardiac ventricular cells. L-type Ca2+ channels were activated by depolarization of cell-attached membrane patches, and [Ca2+](i) was measured simultaneously as fluo 3 fluorescence using laser scanning confocal microscopy. Patch depolarization with Ca2+ as the charge career (10 or 110 mmol · L-1) significantly increased the probability of the occurrence of Ca12+ sparks (Ca2+ spark rate) only in the volume of cytoplasm located immediately beneath the membrane patch (basal Ca2+ spark rate, 119 Ca2+ sparks · cell- · s-1; patch depolarization Ca2+ spark rate, 610 Ca2+ sparks · cell-1 · s-1; P<.005). With Ba2+ in the pipette solution (10 mmol · L-1), patch depolarization was not associated with an increased Ca2+ spark rate at the position of the pipette or at any other sites distant from the pipette. Therefore, Ca2+ entry and not voltage per se was a necessary event for the occurrence of Ca2+ sparks. Under identical experimental conditions, patch depolarization experiments opened single L-type Ca2+ channels with a single-channel conductance of 19 pS with Ba2+ as the charge career. Although single-channel openings could not be resolved when Ca2+ was the charge carrier, ensemble averages yielded an inward current of up to 0.75 pA. The results suggest that voltage-activated Ca2+ entry through one or a small number of L type Ca2+ channels triggers the release of Ca2+ only from the sarcoplasmic reticulum in direct proximity to those L-type Ca2+ channels. The relatively low probability of triggering Ca2+ sparks may have resulted from some alteration of excitation-contraction coupling associated with the technique of the cell- attached patch clamp.

Original languageEnglish
Pages (from-to)424-429
Number of pages6
JournalCirculation research
Issue number4
StatePublished - Mar 9 1998


  • Ca spark
  • Excitation-contraction coupling
  • Heart
  • Single L-type Ca channel


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