Effect of hyperthermia in vitro on stress protein synthesisand accumulation in oyster haemocytes

Haemocytes comprise a major component of the non-specific defence mechanismsin marine bivalves. Induction of stress protein (SP) synthesis and accumulation of SPs was studied in vitro to define the metabolic response of oyster (C. virginica) haemocytes to acute temperature changes. An acute cold shock to near freezing had no significant effect on protein synthesis. However, a comparable heat shock of 20–28° C above the acclimation temperature of 20° C provoked a robust increase in synthesis of several SPs, especially those of about 70 (SP70), 37, 34 and 32 kDa. This response persisted for at least 24 h, during which time both isoforms of SP70-like immunoreactivity accumulated. Concomitantly, there was a decrease in the synthesis, but not in the level, of an actin-like protein of about 45 kDa. The extent of SP synthesis induction also was directly dependent on the duration of the preceding hyperthermia. Extending the duration of heat shock necessitated a longer recovery period, during which time amino acid incorporation returned towards or beyond the initial control values and cell viability was retained. After a severe heat shock at 46° C for 1 h, the predominant protein made for several days was SP70, which is known to be essential for stress tolerance in other biological systems. The results suggest that oyster haemocytes are remarkably resilient, and that SPs may contribute to their ability to resist or repair heat-evoked damage. This molecular adaptability could permit them to maintain immune surveillance during or immediately following serious threats to survival of these sessile ectotherms.