HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Movie Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Curtis, T. M. Articles by McGeown, J. G. Search for Related Content PubMed PubMed Citation Articles by Curtis, T. M. Articles by McGeown, J. G.

Identification and Spatiotemporal Characterization of Spontaneous Ca²⁺ Sparks and Global Ca²⁺ Oscillations in Retinal Arteriolar Smooth Muscle Cells

¹From the Ophthalmic Research Centre, The Queen’s University of Belfast, Institute of Clinical Sciences, The Royal Victoria Hospital, Belfast, Northern Ireland; and the ²Smooth Muscle Group, The Queen’s University of Belfast, Medical Biology Centre, Belfast, Northern Ireland.

PURPOSE. To identify spontaneous Ca²⁺ sparks and global Ca²⁺ oscillations in microvascular smooth muscle (MVSM) cells within intact retinal arterioles and to characterize their spatiotemporal properties and physiological functions.

METHODS. Retinal arterioles were mechanically dispersed from freshly isolated rat retinas and loaded with Fluo-4, a Ca²⁺-sensitive dye. Changes in [Ca²⁺]_i were imaged in MVSM cells in situ by confocal scanning laser microscopy in x-y mode or line-scan mode.

RESULTS. The x-y scans revealed discretely localized, spontaneous Ca²⁺ events resembling Ca²⁺ sparks and more global and prolonged Ca²⁺ transients, which sometimes led to cell contraction. In line scans, Ca²⁺ sparks were similar to those previously described in other types of smooth muscle, with an amplitude (F/F₀) 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 µm, and frequency of 0.56 ± 0.06 seconds^–1. Approximately 35% of sparks had a prolonged tail (>80 ms), similar to the Ca²⁺"embers" described in skeletal muscle. Sparks often summated to generate global and prolonged Ca²⁺ elevations on which Ca²⁺ sparks were superimposed. These sparks occurred more frequently (2.86 ± 025 seconds^–1) and spread farther across the cell (FWHM = 1.67 ± 0.08 µm), but were smaller (F/F₀ = 0.69 ± 0.04).

CONCLUSIONS. Retinal arterioles generate Ca²⁺ sparks with characteristics that vary during different phases of the spontaneous Ca²⁺-signaling cycle. Sparks summate to produce sustained Ca²⁺ transients associated with contraction and thus may play an important excitatory role in initiating vessel constriction. This deserves further study, not least because Ca²⁺ sparks appear to inhibit contraction in many other smooth muscle cells.

This article has been cited by other articles:

				M. K. McGahon, D. P. Dash, A. Arora, N. Wall, J. Dawicki, D. A. Simpson, C. N. Scholfield, J. G. McGeown, and T. M. Curtis Diabetes Downregulates Large-Conductance Ca2+-Activated Potassium {beta}1 Channel Subunit in Retinal Arteriolar Smooth Muscle Circ. Res., March 16, 2007; 100(5): 703 - 711. [Abstract] [Full Text] [PDF]

				S.-Z. Xu, G. Boulay, R. Flemming, and D. J. Beech E3-targeted anti-TRPC5 antibody inhibits store-operated calcium entry in freshly isolated pial arterioles Am J Physiol Heart Circ Physiol, December 1, 2006; 291(6): H2653 - H2659. [Abstract] [Full Text] [PDF]

				M. K. McGahon, J. M. Dawicki, C. N. Scholfield, J. G. McGeown, and T. M. Curtis A-Type Potassium Current in Retinal Arteriolar Smooth Muscle Cells Invest. Ophthalmol. Vis. Sci., September 1, 2005; 46(9): 3281 - 3287. [Abstract] [Full Text] [PDF]