Lipoproteins and heat shock proteins as measures of reproductive physiology in the soft shell clam, Mya arenaria

Abstract

Reproduction is an important physiological process in marine bivalve molluscs. Experiments were designed to examine the role of lipoproteins and heat shock proteins in normal physiological processes of the soft shell clam, Mya arenaria, including reproduction. The distribution of 14c triolein, an injected lipid tracer, occurred rapidly and was unaffected by the early stages of the disease hematopoietic neoplasia. These results, in combination with other evidence, provide support for the hypothesis that plasma is the primary conduit for lipid transport in the soft shell clam. A very high density lipoprotein (VHDL) was isolated from clam plasma. The association of only small amounts of the lipid tracer with the VHDL suggest that it may not play a large role in lipid transport. The lack of information on the turnover rate of the lipoprotein, however, makes this result uncertain. Additionally, the expression of the heat shock protein 70 family was measured in the gill and gonad of clams from severely (New Bedford Harbor), moderately (Cotuit Bay), and negligibly (Little Buttermilk Bay) contaminated natural populations. Site differences in hsp 70 expression were observed only in the gill of clams from the New Bedford Harbor population, suggesting that a threshold exists for the induction of the stress response. Effects of the reproductive cycle, however, were observed in both gill and gonad tissues. In New Bedford Harbor, the stress associated with the later stages of the reproductive cycle (ripe, spawning, and spent) appears to interact synergistically with the contaminant effect. The interpretation of a stress response associated with exposure to environmental contaminants, therefore, must include a careful consideration of the effect of natural physiological processes, including reproduction, on the expression of hsp 70.