Extracellular lactate as a dynamic vasoactive signal in the rat retinal microvasculature.
We tested the hypothesis that extracellular lactate regulates the function of pericyte-containing retinal microvessels. Although abluminally positioned pericytes appear to adjust capillary perfusion by contracting and relaxing, knowledge of the molecular signals that regulate the contractility of these mural cells is limited. Here, we focused on lactate because this metabolic product is in the retinal extracellular space under both physiological and pathophysiological conditions. In microvessels freshly isolated from the adult rat retina, we used perforated-patch pipettes to monitor ionic currents, fura-2 to measure calcium levels, and time-lapse photography to visualize changes in mural cell contractility and lumen diameter. During lactate exposure, pericyte calcium rose; these cells contracted, and lumens constricted. This contractile response appears to involve a cascade of events resulting in the inhibition of Na+/Ca2+ exchangers (NCXs), the decreased of which function causes pericyte calcium to increase and contraction to be triggered. On the basis of our observation that gap junction uncouplers minimized the lactate-induced rise in pericyte calcium, we propose that the NCXs inhibited by lactate are predominately located in the endothelium. Indicative of the importance of endothelial/pericyte gap junctions, uncouplers of these junctions switched the pericyte response to lactate from contraction to relaxation. In addition, we observed that hypoxia, which closes microvascular gap junctions, also switched lactate's effect from vasocontraction to vasorelaxation. Thus the response of pericyte-containing retinal microvessels to extracellular lactate is metabolically modulated. The ability of lactate to serve as a vasoconstrictor when energy supplies are ample and a vasodilator under hypoxic conditions may be an efficient mechanism to link capillary function with local metabolic need.
Yamanishi
Shigeki
S
Department of Ophthalmology and Visual Sciences, University of Michigan, 1000 Wall St., Ann Arbor, Michigan 48105, USA.
Katsumura
Kozo
K
Kobayashi
Takatoshi
T
Puro
Donald G
DG
D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology; D005246:Feedback / Q000187:drug effects / Q000502:physiology; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology*; D006487:Hemostasis / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D019344:Lactic Acid / Q000494:pharmacology*; D008833:Microcirculation / Q000187:drug effects / Q000502:physiology*; D020286:Pericytes / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D012171:Retinal Vessels / Q000187:drug effects / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014666:Vasomotor System / Q000187:drug effects / Q000502:physiology
D014662:Vasoconstrictor Agents; D019344:Lactic Acid; D002118:Calcium