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K. Matsushita, D.G. Puro; Inwardly Rectifying Potassium Currents in Rat Retinal Microvessels . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2993.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Potassium released from glial cells at sites adjacent to blood vessels is a putative vasoactive signal. Our goal is to identify mechanisms by which K+ affects the physiology of pericyte–containing retinal microvessels, which are likely to play a role in the regulation of local vascular perfusion. Methods: Pericyte–containing microvessels were isolated from the adult rat retina by first exposing a retina to papain, then gently pressing it between two glass coverslips; complexes of retinal microvessels adhered to the glass. Experiments were done within 3h of vessel isolation. Ionic currents were monitored in pericytes via perforated–patch pipettes. Results: Inwardly rectifying currents were detected in pericytes located on freshly isolated retinal capillaries. The I–V relationship showed steep inward rectification. Consistent with a selective permeability to potassium, the reversal potential of these currents was near the equilibrium potential for K+. In addition, as is well known for KIR channels, barium reversibly inhibited the inwardly rectifying current recorded in pericytes. We also observed that with increases in [K+]o, the conductance of this inward current in pericytes increased, as it does in cells known to express KIR channels. Suggestive of a topographical distribution within the pericyte–containing microvasculature, steeply rectifying KIR currents were detected in retinal pericytes located on isolated capillaries, but appear to be less prominent in pericyte–containing pre– and post–capillaries. Conclusions: Pericytes on retinal capillaries express functional KIR channels. The steep inwardly rectifying nature of these channels suggests that they would minimally impede the pericyte depolarization that is caused by the opening of non–specific cation channels during exposure of retinal microvessels to endothelin–1, extracellular ATP and angiotensin II (Kawamura et al., 2002, 2003; in press). On the other hand, these KIR channels would provide high conductance pathways for an influx of K+ at focal sites where [K+]o is elevated and potassium serves as a vasoactive signal.
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