A function for pericardial cells in an insect

The pericardial cells (PCs) of fifth instar Calpodes ethlius larvae are functionally adapted for filtering hemolymph and sequestering and digesting proteins. They also have a structure appropriate for the synthesis of proteins for secretion. PC secretion has been investigated by labelling the cells with [³⁵S]methionine ti vitro with detection of newly synthesized polypeptides appearing in the medium by electrophoresis and fluorography. Sources possibly contributing to the appearance of newly synthesized polypeptides in the medium, such as cell breakdown and fat body contamination have been ruled out. The post-incubation medium of PCs contains at least six newly synthesized polypeptides. Three of these polypeptides, having relative molecular masses of 82, 57 and 43 kDa, react with antibodies to hemolymph. At least one additional polypeptide is similar by two-dimensional analysis to that naturally present in hemolymph. PCs incubated together with the heart to which they are normally attached, secrete additional polypeptides that are presumed to come from the heart. The 82 kDa polypeptide secreted by the PCs is similar to the subunits of arylphorin secreted by fat body and other tissues. We conclude that PCs secrete proteins into the hemolymph although the amount may be small relative to that of the fat body.