title: Ca2+ sparks triggered by patch depolarization in rat heart cells.
abstract: 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 carrier (10 or 110 mmol.L(-1)) significantly increased the probability of the occurrence of Ca2+ sparks (Ca2+ spark rate) only in the volume of cytoplasm located immediately beneath the membrane patch (basal Ca2+ spark rate, 119 Ca2+ sparks.cell(-1).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 carrier. 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.
authors.affiliation: Department of Medicine, University of Maryland School of Medicine, Baltimore 21201, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Shorofsky
authors.forename: L
authors.initials: L
authors.lastname: Izu
authors.forename: W G
authors.initials: WG
authors.lastname: Wier
authors.forename: C W
authors.initials: CW
authors.lastname: Balke
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D006321:Heart / Q000502:physiology*; D015640:Ion Channel Gating; D008564:Membrane Potentials; D018613:Microscopy, Confocal; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D012508:Sarcolemma / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000502:physiology
chemical_list: D002118:Calcium