Characterisation of glycoproteins in the secretory cells in the operculum of an Indian hill stream fish Garra lamta (Hamilton) (Cyprinidae, Cypriniformes)

Abstract

Glycoproteins (GPs) elaborated by the secretory cells in the opercular epidermis (OE) and the epithelium lining the inner surface of the operculum (EISO), of an Indian hill stream fish Garra lamta have been analysed by means of a battery of histochemical methods. These included methods for the characterisation and simultaneous visualisation of GPs with oxidizable vicinal diols, O-acyl sugars, O-sulphate esters and sialic acid residues without O-acyl substitution or with O-acyl substitution at C7, C8 or C9. Results obtained in this study show that conventional periodic acid Schiff's and alcian blue based procedures are less sensitive and largely fail to identify different classes of GPs. In the OE the secretory cells involved in the synthesis of GPs are the epithelial cells, the mucous cells and the club cells. Based on the histochemical characterisation of GPs, the mucous cells are distinguished in to two types, Type A and Type B. The majority being of Type A. In the EISO, in contrast, the club cells are absent and most mucous cells belong to a third category, Type C. Type A and Type B mucous cells are few. GP classes synthesised by the secretory cells and released on the outer surface of the operculum, directly exposed to the environmental hazards show significant differences in their composition and concentration from those on, the relatively well protected, inner surface of the operculum. These are discussed in relation to the physiological significance of the GP classes with special reference to their role in lubrication, protection and inhibition of the invasion and proliferation of pathogenic micro-organisms.