Bao, RongfengLifshitz, Lawrence M.Tuft, Richard A.Bellve, Karl D.Fogarty, Kevin E.ZhuGe, Ronghua2022-08-232022-08-232008-07-022009-10-15J Gen Physiol. 2008 Jul;132(1):145-60. <a href="http://dx.doi.org/10.1085/jgp.200709933">Link to article on publisher's site</a>1540-7748 (Electronic)10.1085/jgp.20070993318591421https://hdl.handle.net/20.500.14038/39087Ca(2+) sparks are highly localized, transient releases of Ca(2+) from sarcoplasmic reticulum through ryanodine receptors (RyRs). In smooth muscle, Ca(2+) sparks trigger spontaneous transient outward currents (STOCs) by opening nearby clusters of large-conductance Ca(2+)-activated K(+) channels, and also gate Ca(2+)-activated Cl(-) (Cl((Ca))) channels to induce spontaneous transient inward currents (STICs). While the molecular mechanisms underlying the activation of STOCs by Ca(2+) sparks is well understood, little information is available on how Ca(2+) sparks activate STICs. In the present study, we investigated the spatial organization of RyRs and Cl((Ca)) channels in spark sites in airway myocytes from mouse. Ca(2+) sparks and STICs were simultaneously recorded, respectively, with high-speed, widefield digital microscopy and whole-cell patch-clamp. An image-based approach was applied to measure the Ca(2+) current underlying a Ca(2+) spark (I(Ca(spark))), with an appropriate correction for endogenous fixed Ca(2+) buffer, which was characterized by flash photolysis of NPEGTA. We found that I(Ca(spark)) rises to a peak in 9 ms and decays with a single exponential with a time constant of 12 ms, suggesting that Ca(2+) sparks result from the nonsimultaneous opening and closure of multiple RyRs. The onset of the STIC lags the onset of the I(Ca(spark)) by less than 3 ms, and its rising phase matches the duration of the I(Ca(spark)). We further determined that Cl((Ca)) channels on average are exposed to a [Ca(2+)] of 2.4 microM or greater during Ca(2+) sparks. The area of the plasma membrane reaching this level is <600 nm in>radius, as revealed by the spatiotemporal profile of [Ca(2+)] produced by a reaction-diffusion simulation with measured I(Ca(spark)). Finally we estimated that the number of Cl((Ca)) channels localized in Ca(2+) spark sites could account for all the Cl((Ca)) channels in the entire cell. Taken together these results lead us to propose a model in which RyRs and Cl((Ca)) channels in Ca(2+) spark sites localize near to each other, and, moreover, Cl((Ca)) channels concentrate in an area with a radius of approximately 600 nm, where their density reaches as high as 300 channels/microm(2). This model reveals that Cl((Ca)) channels are tightly controlled by Ca(2+) sparks via local Ca(2+) signaling.en-USAniline CompoundsAnimalsCalciumCalcium SignalingCells, CulturedChloride ChannelsComputer SimulationEgtazic AcidElectrophysiologyKineticsMaleMembrane PotentialsMiceModels, BiologicalMuscle, SmoothMyocytes, Smooth MusclePhotolysisRyanodine Receptor Calcium Release ChannelTracheaXanthenesLife SciencesMedicine and Health SciencesJournal Articlehttps://escholarship.umassmed.edu/cgi/viewcontent.cgi?article=2904&amp;context=oapubs&amp;unstamped=1https://escholarship.umassmed.edu/oapubs/19051036648oapubs/1905