Abstract
Objective: Little is known about the electrotonic architecture of the pericyte-containing retinal microvasculature. Here, the authors focus on the cell-to-cell transmission of hyperpolarization, which can induce abluminal pericytes to relax and lumens to dilate.
Methods: With perforated-patch pipettes, the authors monitored the membrane potentials and ionic currents of pairs of pericytes located on freshly isolated rat retinal microvessels. Voltage changes were induced by administering electrical stimuli into pericytes, miniperfusing the KATP channel opener pinacidil, or using oxotremorine to activate chloride channels.
Results: Suggestive of extensive cell-to-cell communication, spontaneous voltage changes were strikingly similar in widely separated pericytes. In addition, injection of current into one of a pair of sampled pericytes always elicited a voltage response in the other sampled pericyte; the gap junction uncoupler, heptanol, blocked this transmission. In the dual recordings, hyperpolarization spreading from a current-injected pericyte decayed ∼40% within 100 μ m. In contrast, pinacidil-induced hyperpolarizations diminished by only ∼ 2% in 100 μ m. Depolarizations also appeared to spread with similar transmission efficacies.
Conclusions: Based on the experiments, the authors propose that key features of the electrotonic architecture of retinal microvessels include highly efficient cell-to-cell communication within the endothelium and relatively inefficient transmission at pericyte/endothelial junctions. Thus, the endothelium is likely to provide an efficient pathway that functionally links contractile pericytes and thereby, serves to coordinate the vasomotor response of a retinal capillary.
Grant support: The authors thank Bret A. Hughes and Daniel G. Green for helpful comments. This project was supported by grants EY12505 and EY07003 from the National Institutes of Health. D.W. received a Physician-Scientist Training Award from the American Diabetes Association and a Research to Prevent Blindness Medical Student Research Fellowship. D.G.P. is a Research to Prevent Blindness Senior Scientific Scholar.