LOCALIZATION OF RYANODINE RECEPTORS IN SMOOTH-MUSCLE

1The ryanodine receptor (RyR) in aortic and vas deferens smooth muscle was localized using immunofluorescence confocal microscopy and immuno electron microscopy, Indirect immunofluorescent labeling of aortic smo oth muscle with anti-RyR antibodies showed a patchy network-like stain ing pattern throughout the cell cytoplasm, excluding nuclei, in aortic smooth muscle and localized predominantly to the cell periphery in th e vas deferens. This distribution is consistent with that of the sarco plasmic reticulum (SR) network, as demonstrated by electron micrograph s osmium ferrocyanide-stained SR in the two smooth muscles. Immunoelec tron microscopy of vas deferens smooth muscle showed anti-RyR antibodi es localized to both the sparse central and predominant peripheral SR elements, We conclude that RyR-Ca2+-release channels are present in bo th the peripheral and central SR in aortic and vas deferens smooth mus cle, This distribution is consistent with the possibility that both re gions are release sites, as indicated by results of electron probe ana lysis, which show a decrease in the Ca2+ content of both peripheral an d internal SR in stimulated smooth muscles, The complex distribution o i inositol 1,4,5-trisphosphate and ryanodine receptors (present study) is compatible with their proposed roles as agonist-induced Ca2+-relea se channels and origins of Ca2+ sparks, Ca2+ oscillations, and Ca2+ wa ves.