The conus arteriosus of the adult gilthead seabream (Sparus auratus)

Abstract

This paper reports on the presence of the conus arteriosus in the heart of the adult gilthead seabream, Sparus auratus (Perciformes, Teleostei). The junctional region between the single ventricle and the bulbus arteriosus has been studied by conventional light microscopy, and by scanning and transmission electron microscopy. In addition, fluorescent phalloidin and antibodies against the muscle myosin heavy chains, laminin and collagen type IV have been used. The conus arteriosus is a distinct muscular segment interposed between the ventricle and the bulbus arteriosus. It is clearly different from the bulbus arteriosus due to its myocardial nature. It can also be distinguished from the ventricular myocardium because: (1) it has a conus shape; (2) it is formed by compact, well-vascularized myocardium; (3) it is surrounded on its inner and outer faces by fibrous layers rich in collagen and elastin; (4) it constitutes the anatomical support of the so-termed conus valves; (5) it shows intense staining for laminin and type-IV collagen; and (6) the myocardial cells located close to the inner fibrous layer are helicoidally arranged. By contrast, the ventricular myocardium is highly trabecular, lacks a compacta, shows no vessels, and presents barely detectable amounts of laminin and collagen type IV. The presence of a distinct conus arteriosus in the heart of an evolutionary advanced teleost species indicates that the conus is not a vestigial segment from the evolutionary or embryological points of view. The characteristic spatial arrangement of the conus myocytes strongly suggests that the conus is implicated in the mechanical performance of the conus valves.

The extracellular matrix of Gadus morhua muscle contains types III, V, VI and IV collagens in addition to type I

“…Collagen IV is the major collagen of this structure and regulates cell adhesion and migration. Although collagen IV has not been previously shown in fish swimming muscle, Schib et al (2002) clearly illustrated its presence in the basement membrane of heart muscle of Sparus aurata L. The development of a muscle fibre basement membrane can be concluded from immuno-staining for laminin in developing zebrafish Danio rerio (Hamilton) (Parsons et al, 2002). Due to structural similarities between mammalian and fish muscle, it would be surprising not to find functional basement membranes in the swimming muscles of different fish species.…”

Chondrichthyans have a bulbus arteriosus at the arterial pole of the heart: morphological and evolutionary implications

“…It has been generally assumed that in most teleosts, the conus arteriosus is vestigial or even absent, a fact that has been considered to be concomitant with the remarkable development of the bulbus arteriosus in this zoological group (Smith, 1918; Santer, 1985; Satchell, 1991; Farrell & Jones, 1992). In contrast to this traditional viewpoint, recent studies indicate that the conus, although reduced in size, exists almost certainly in the majority or even in all teleost species, being actively implicated in the performance of the conal valves (Schib et al. 2002; Icardo et al.…”

Phylogeny informs ontogeny: a proposed common theme in the arterial pole of the vertebrate heart

“…In contrast, in the chondrichthyans (sharks, skates, and rays), whereas there is an embryonic conus arteriosus that may be homologous to the common outflow of the avian and mammalian embryo (see Romer and Parsons 1986; Holmes 2005; Moorman et al 2007), this structure persists into adulthood and is never incorporated into the ventricle. On the other hand, although similarly a homologous conus arteriosus undoubtedly exists in the embryonic heart of at least the vast majority of apical teleosts (see Schib et al 2002; Guerrero et al 2004; Grimes et al 2006; Icardo 2006; Grimes and Kirby 2009), the fact that it regresses toward and, in most cases, appears to be incorporated into the ventricle later in development means that it is not obvious in adult forms, except under careful histological scrutiny (see Grimes et al 2006; Icardo 2006). This has resulted in the structure being described as merely vestigial or even missing entirely in many descriptions of the teleost heart (e.g., Satchell 1991; Farrell and Jones 1992).…”