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E. Abad, M. Morales, J. Pales, A. Gual, X. Gasull; Characterization of Store–Operated Ca2+ Influx in Trabecular Meshwork Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1849.
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In non–excitable cells, the major Ca2+ entry pathway is the store–operated (capacitative) Ca2+ influx, which activates after the emptying of intracellular Ca2+ stores. Store–operated Ca2+ influx participates in cell Ca2+ homeostasis as well as in different processes related to cell growth and differentiation, enzyme control or exocytosis. Moreover, store–operated Ca2+ influx appears to be involved in cellular contractility and regulation of vascular smooth muscle tone. Since trabecular meshwork (TM) contractility modulates outflow facility, we studied the presence and characteristics of store–operated Ca2+ influx in TM cells as a possible regulator of this tissue function.
Primary cultures of bovine TM cells were used. Intracellular calcium concentration ([Ca2+]i) was measured in TM cells loaded with Fura–2. Store–operated calcium currents were characterized using the whole–cell configuration of the patch clamp technique.
Bradykinin evoked a biphasic increase in [Ca2+]i: an initial Ca2+ release from intracellular stores followed by a sustained extracellular Ca2+ influx. Ca2+ influx was greatly reduced when extracellular Ca2+ was removed or in the presence of 2–APB, a blocker of store–operated Ca2+ channels. Similar results were obtained with endothelin–1 stimulation. After intracellular stores depletion with thapsigargin (in Ca2+–free solution), reintroduction of extracellular Ca2+ produced a secondary Ca2+ influx that could be prevented by preincubation with 2–APB or La3+. In patch–clamp recordings, depletion of intracellular stores with IP3 + EGTA or with thapsigargin induced a non–voltage–gated inward current with the properties described for store–operated Ca2+ currents.
TM cells possess store–operated Ca2+ currents that appears to participate in the intracellular Ca2+ increments induced by different hormones or neurotransmitters. Block of Ca2+ influx by 2–APB and La3+ suggests the involvement of TRPC channels. Their participation in TM outflow regulation is under current study.
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