CILIARY MUSCLE CAPILLARIES HAVE BLOOD-TISSUE BARRIER CHARACTERISTICS

It was determined whether the capillaries in the ciliary muscle are of the blood-tissue barrier or of the permeable non-barrier type. Ciliar y body and iris of normal human and animal eyes were examined by elect ron microscopy and by immunohistochemical staining with a panel of ant ibodies recognizing endothelial blood-brain barrier markers. In additi on. horseradish peroxidase (HRP) tracer studies of the anterior segmen t were carried out in rabbits. Our results demonstrated that the capil lary endothelium in human and rabbit ciliary muscle has few luminal pi nocytotic vesicles and a morphological aspect suggesting the presence of tight junctions. Ciliary muscle and iris capillaries stained positi ve for the blood-brain barrier markers Glucose-Transporter-1 and P-Gly coprotein, while staining for the PAL-E antigen and the transferrin re ceptor was absent. In the rabbit ciliary muscle, vascular leakage of e xogenous HRP tracer was absent. It was concluded that this functional barrier and the observed phenotype of ciliary muscle capillaries are c onsistent with a blood-tissue barrier function similar to that of the iris microvasculature. (C) 1998 Academic Press.