Ultrastructure of the capillary pericytes and the expression of smooth muscle α-actin and desmin in the snake infrared sensory organs

Abstract

The infrared sensory membranes of pit organs of pit vipers have an extremely rich capillary vasculature that forms many vascular loops, each serving a small number of infrared nerve terminals. We clarified the ultrastructure of capillary pericytes in the pit membranes by scanning and transmission electron microscopy, and examined the immunoreactivity in their cytoplasm to two contractile proteins: smooth muscle α‐actin (SM α‐actin) and desmin. The capillary pericytes had two major cytoplasmic processes: thickened primary processes that radiate to embrace the endothelial tube and flattened secondary processes that are distributed widely on the endothelium. Coexpression of SM α‐actin and desmin was observed in the pericytes of entire capillary segments, and SM α‐actin was characterized by prominent filament bundles directed mainly at right angles to the capillary long axis. This expression pattern was different from that of capillary pericytes of the scales, where SM α‐actin was expressed diffusely in the cytoplasm. In a series of electron microscopic sections, we often observed the pericyte processes depressing the endothelial wall. We also observed a close relationship of the pericytes with inter‐endothelial cell junctions, and pericyte processes connected with the endothelial cells via gap junctions. From these findings, we surmised that capillary pericytes in the pit membrane have a close functional relationship with the endothelium, and through their contractile and relaxing activity regulate capillary bloodflow to stabilize production of infrared nerve impulses. Anat Rec 260:299–307, 2000. © 2000 Wiley‐Liss, Inc.

Distribution of myelinated and unmyelinated nerve fibers and their possible role in blood flow control in crotaline snake infrared receptor organs

“…Goris et al (2000) speculated that the capillary pericytes were induced to relax and, thus, speed up blood flow, by a vasodilator such as nitric oxide (NO) released directly by the TNMs themselves when stimulated. Nakano et al (2000) showed that blood flow could be regulated by relaxation and contraction of capillary pericytes under the influence of such a vasodilator.…”

“…The pit membrane has a denser capillary network than any other area of skin, and the TNMs all are closely apposed to capillaries. In addition to supplying oxygen to the TNMs, the capillary network is also thought to erase infrared afterimages by cooling the TNMs (Amemiya et al, 1999; Nakano et al, 2000; Goris et al, 2000; Kishida et al, 2001).…”

Signaling at the Gliovascular Interface

“…The pockets of the inner membrane of the basal lamina contained desmin-positive pericytessmooth muscle cells (Fig. 7C) (Diaz-Flores et al, 1991;Nakano et al, 2000). The pericytes are elongated cells forming a fibrous network surrounding larger vessels (Fig.…”

Pivotal role of pericytes in kidney fibrosis

“…For more than 100 years since they were described, 15,16 pericytes were considered to be contractile cells regulating vascular tone and blood flow because, anatomically, the processes of pericytes envelope EC and pericytes express contractile microfilaments (actin, myosin) and intermediate filaments (desmin, vimentin) 17–19 . Definitive functional studies have proved that pericytes control capillary diameter in whole retina and cerebellar slices 20 .…”