Functional morphology of laminin, collagen type IV, collagen bundles, elastin, and proteoglycans in the bulbus arteriosus of the white bass, Morone chrysops (Rafinesque)

Abstract

Immunolocalization of the basal lamina proteins laminin and collagen type IV, and the distribution of collagen bundles, elastin fibres, and proteoglycans in the bulbus arteriosus of adult white bass, Morone chrysops, were investigated. The bulbus arteriosus consists of three discernible layers: intima, media, and adventitia. The media composes approximately 95% of the bulbus arteriosus volume, and consists of elastin fibres, which allow distensibility, and proteoglycans which may be utilized in dissipating the frictional forces in an actively expanding bulbus arteriosus. Laminin and collagen type IV were co-localized to the luminal and bulbar–ventricular valve subendothelium anchoring the endothelium to the underlying parenchyma. Laminin and collagen IV were also expressed in the adventitia along with prominent collagen bundles which may serve to limit the expansion of the bulbus arteriosus at high intraluminal pressures. Collagen bundles and scattered elastin fibres are longitudinally aligned along the ventricular border of the bulbar–ventricular valve, acting as a semi-stiff border facilitating the timely opening of the valve and buffering the systolic force of inflowing blood. Proteoglycans occupy the bulbar portion of the valve and are most probably involved in absorbing the initial recoil from the front of the valve, thereby decreasing wear and tear upon the valve.