Role of gap junctions in regulating the physiology of retinal pericytes.

Abstract

Abstract: : Purpose: Pericyte–containing microvessels are likely to play an important role in regulating retinal blood flow. Although it is known that there are gap junctions between endothelial cells and pericytes, the role of these intercellular pathways in regulating pericyte function remains unclear. Methods: Papain–treated rat retinas were gently pressed between two glass coverslips. Complexes of retinal microvessels adhered to the glass; experiments were done within 3h. Ionic currents were monitored in pericytes via perforated–patch pipettes. Contractions of pericyte–containing microvessels were visualized with the aid of differential interference optics and time–lapse photography. Results: We used octanol (1mM) or α–glycyrrhetinic acid (100µM) to close gap junctions. Consistent with this action, these chemicals caused the time course for the decay of the membrane capacitive current in sampled pericytes to shorten and to be fit by a single exponential function. With gap junction closure, the pericyte membrane resistance increased markedly (∼20 fold), and the membrane potential hyperpolarized from –37 ± 1 mV to –60 ± 7 mV (n = 10). In addition, exposure to these gap junction uncouplers caused pericytes to contract. Specifically, 42% of the 124 pericytes that were monitored by time–lapse photography contracted in response to octanol or α–glycyrrhetinic acid; none relaxed. Capillary lumens adjacent to contracting pericytes narrowed. These effects were reversible. However, although the hyperpolarization associated with gap junction closure was blocked by ouabain, this potent inhibitor of the Na⁺–K⁺ pump failed (P = 1.0) to prevent pericyte contraction in response to the closing of gap junctions. Conclusions: Intercellular communication via gap junctions significantly influences the physiology of retinal pericytes. By a mechanism that requires open gap junctions, endothelial cells appear to exert a relaxing effect on retinal pericytes. Thus, gap junction closure induced by certain vasoactive molecules (Kawamura et al. 2001) or caused by diabetes (Oku et al., 2001) may play a previously unrecognized role in diminishing capillary perfusion in the retina.

Keywords: gap junctions/coupling • retina • vascular cells