Diabetes-induced disruption of gap junction pathways within the retinal microvasculature

PURPOSE. Microvascular damage caused by diabetes is a leading cause of visu al loss. Identifying events early in the course of diabetic retinopathy may help in understanding and, perhaps, preventing this disorder. The hypothes is that cell-to-cell communication within the retinal microvasculature may be affected soon after the onset of diabetes was tested. METHODS. Streptozotocin was used to induce diabetes in rats. To assess cell -to-cell coupling the gap junction-permeant tracer, Neurobiotin, was delive red via patch pipettes into pericytes located on microvessels freshly isola ted from the retinas of diabetic and control animals. Subsequently, immunoh istochemical methods revealed the extent of the intercellular spread of the tracer. Electrophysiological methods were also used to detect intercellula r communication. RESULTS. In retinal microvessels of control rats, Neurobiotin spread hundre ds of micrometers from the tracer-loaded pericytes. However, within days af ter the onset of diabetes, this cell-to-cell coupling was dramatically redu ced. In contrast, microvessels of insulin-treated diabetic rats showed no s ignificant loss of intercellular communication. Consistent with protein kin ase C (PKC) playing a role in the diabetes-induced inhibition of gap juncti on pathways, exposure of microvessels to a PKC activator (phorbol myristatr acetate) markedly reduced tracer coupling. CONCLUSIONS. Within retinal microvessels there is extensive cell-to-cell co upling, which is markedly reduced soon after the onset of streptozotocin-in duced diabetes. The closure of gap junction pathways disrupts the multicell ular organization of retinal microvessels and may contribute to vascular dy sfunction.