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

Abstract

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.

Endothelin 1 Stimulates Ca2+-Sparks and Oscillations in Retinal Arteriolar Myocytes via IP3R and RyR-Dependent Ca2+Release

“…19,20 Although the term oscillation has been used to describe all prolonged elevations in [Ca 2ϩ ] (Ͼ0.5 seconds), these cannot be distinguished from propagating Ca 2ϩ -waves in transverse line scan recordings. The time course of changes in F/F 0 , spatially averaged across the width of each cell, was plotted using ImageJ software (developed by Wayne Rasband, National…”

“…We have previously reported that high-speed Ca 2ϩ -imaging reveals brief, localized subcellular Ca 2ϩ -signals known as Ca 2ϩ -sparks in both rat and pig retinal arterioles 20,21 ( Fig. 2A).…”

“…20 Briefly, rats were euthanatized in compliance with UK Home Office regulations and the standards set out in the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Retinas were triturated in low-Ca 2ϩ (100 M) Hanks solution, centrifuged, washed, and centri-fuged again.…”

“…An agonist-induced increase in spark frequency in the context of increased oscillation frequency is consistent with our previous studies showing that sparks can summate to produce more prolonged oscillations and that these can activate cell contraction. 19,20 The vasoconstrictor thromboxane analog U46619 has also been shown to stimulate Ca 2ϩ -oscillations in vascular smooth muscle from porcine retinal arterioles, though only at low extracellular [Ca 2ϩ ], suggesting other signaling mechanisms may be involved under more physiological conditions. 39 Pharmacologic interventions that modulate spark activity in rat retinal arteriolar smooth muscle produce positively correlated changes in Ca 2ϩ -oscillations, and the stimulation of oscillations in porcine retinal arterioles with the constrictor agonist AVP was also associated with an increase in Ca 2ϩ -sparks.…”

E3-targeted anti-TRPC5 antibody inhibits store-operated calcium entry in freshly isolated pial arterioles

“…Nevertheless, significant progress has been made, particularly toward understanding mechanisms of rhythmicity, myogenic tone, and ion transport (11,12,14,17,20,25,26,31,33,34). An area of particular interest is calcium signaling (10,15,26,38). Calcium has a pivotal role in regulating contraction but also emerging importance as a regulator of gene expression and cellular phenotype (2,50).…”