Ca2+ Sparks Triggered by Patch Depolarization in Rat Heart Cells

    loading  Checking for direct PDF access through Ovid

Abstract

The goal of this study was to examine the relationship between Ca (2+) 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 conforcal microscopy. Patch depolarization with Ca2+ as the charge carrier (10 or 110 mmol [center dot] 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 [center dot] cell-1 [center dot] s-1; patch depolarization Ca2+ spark rate, 610 Ca2+ sparks [center dot] cell-1 [center dot] s-1; P<.005). With Ba2+ in the pipette solution (10 mmol [center dot] 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. (Circ Res. 1998;82:424-429.)

Related Topics

    loading  Loading Related Articles