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Identification and spatiotemporal characterization of spontaneous Ca2+ sparks and global Ca2+ oscillations in retinal arteriolar smooth muscle cells.

ABSTRACT: To identify spontaneous Ca(2+) sparks and global Ca(2+) oscillations in microvascular smooth muscle (MVSM) cells within intact retinal arterioles and to characterize their spatiotemporal properties and physiological functions.Retinal arterioles were mechanically dispersed from freshly isolated rat retinas and loaded with Fluo-4, a Ca(2+)-sensitive dye. Changes in [Ca(2+)](i) were imaged in MVSM cells in situ by confocal scanning laser microscopy in x-y mode or line-scan mode.The x-y scans revealed discretely localized, spontaneous Ca(2+) events resembling Ca(2+) sparks and more global and prolonged Ca(2+) transients, which sometimes led to cell contraction. In line scans, Ca(2+) sparks were similar to those previously described in other types of smooth muscle, with an amplitude (DeltaF/F(0)) of 0.81 +/- 0.04 (mean +/- SE), full duration at half maximum (FDHM) of 23.62 +/- 1.15 ms, full width at half maximum (FWHM) of 1.25 +/- 0.05 mum, and frequency of 0.56 +/- 0.06 seconds(-1). Approximately 35% of sparks had a prolonged tail (>80 ms), similar to the Ca(2+)"embers" described in skeletal muscle. Sparks often summated to generate global and prolonged Ca(2+) elevations on which Ca(2+) sparks were superimposed. These sparks occurred more frequently (2.86 +/- 025 seconds(-1)) and spread farther across the cell (FWHM = 1.67 +/- 0.08 microm), but were smaller (DeltaF/F(0) = 0.69 +/- 0.04).Retinal arterioles generate Ca(2+) sparks with characteristics that vary during different phases of the spontaneous Ca(2+)-signaling cycle. Sparks summate to produce sustained Ca(2+) transients associated with contraction and thus may play an important excitatory role in initiating vessel constriction. This deserves further study, not least because Ca(2+) sparks appear to inhibit contraction in many other smooth muscle cells.

SUBMITTER: Curtis TM

PROVIDER: S-EPMC2590679 | biostudies-literature | 2004 Dec

REPOSITORIES: biostudies-literature

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Identification and spatiotemporal characterization of spontaneous Ca2+ sparks and global Ca2+ oscillations in retinal arteriolar smooth muscle cells.

Curtis Tim M TM Tumelty James J Dawicki Jennine J Scholfield C Norman CN McGeown J Graham JG

Investigative ophthalmology & visual science 20041201 12

<h4>Purpose</h4>To identify spontaneous Ca(2+) sparks and global Ca(2+) oscillations in microvascular smooth muscle (MVSM) cells within intact retinal arterioles and to characterize their spatiotemporal properties and physiological functions.<h4>Methods</h4>Retinal arterioles were mechanically dispersed from freshly isolated rat retinas and loaded with Fluo-4, a Ca(2+)-sensitive dye. Changes in [Ca(2+)](i) were imaged in MVSM cells in situ by confocal scanning laser microscopy in x-y mode or lin ...[more]

PMID: 15557449

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Project description:RATIONALE:The development of a refractory period for Ca2+ spark initiation after Ca2+ release in cardiac myocytes should inhibit further Ca2+ release during the action potential plateau. However, Ca2+ release sites that did not initially activate or which have prematurely recovered from refractoriness might release Ca2+ later during the action potential and alter the cell-wide Ca2+ transient. OBJECTIVE:To investigate the possibility of late Ca2+ spark (LCS) activity in intact isolated cardiac myocytes using fast confocal line scanning with improved confocality and signal to noise. METHODS AND RESULTS:We recorded Ca2+ transients from cardiac ventricular myocytes isolated from rabbit hearts. Action potentials were produced by electric stimulation, and rapid solution changes were used to modify the L-type Ca2+ current. After the upstroke of the Ca2+ transient, LCSs were detected which had increased amplitude compared with diastolic Ca2+ sparks. LCS are triggered by both L-type Ca2+ channel activity during the action potential plateau, as well as by the increase of cytosolic Ca2+ associated with the Ca2+ transient itself. Importantly, a mismatch between sarcoplasmic reticulum load and L-type Ca2+ trigger can increase the number of LCS. The likelihood of triggering an LCS also depends on recovery from refractoriness that appears after prior activation. Consequences of LCS include a reduced rate of decline of the Ca2+ transient and, if frequent, formation of microscopic propagating Ca2+ release events (Ca2+ ripples). Ca2+ ripples resemble Ca2+ waves in terms of local propagation velocity but spread for only a short distance because of limited regeneration. CONCLUSIONS:These new types of Ca2+ signaling behavior extend our understanding of Ca2+-mediated signaling. LCS may provide an arrhythmogenic substrate by slowing the Ca2+ transient decline, as well as by amplifying maintained Ca2+ current effects on intracellular Ca2+ and consequently Na+/Ca2+ exchange current.

Dataset Information

Identification and spatiotemporal characterization of spontaneous Ca2+ sparks and global Ca2+ oscillations in retinal arteriolar smooth muscle cells.

Publications

Identification and spatiotemporal characterization of spontaneous Ca2+ sparks and global Ca2+ oscillations in retinal arteriolar smooth muscle cells.

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