SYNTHESIS OF STRESS PROTEIN-70 (HSP70) IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) RED-BLOOD-CELLS

Unlike enucleated mammalian red blood cells (rbcs), the nucleated rbcs of lower vertebrates are capable of protein synthesis and may, theref ore, serve as a valuable model to investigate the adaptive significanc e of stress protein synthesis in cells, This study examined the synthe sis of stress protein 70 (Hsp70) in rbcs of the temperature-sensitive rainbow trout Oncorhynchus mykiss in response to heat shock and anoxia , Through western blot analysis, we have demonstrated that rainbow tro ut rbcs synthesize Hsp7O both constitutively and in response to an inc rease in temperature, Radioisotopic labelling experiments indicated th at the temperature at which Hsp70 synthesis was induced in fish acclim ated to 10 degrees C was between 20 and 25 degrees C, Actinomycin D bl ocked de novo Hsp70 synthesis, implying that synthesis of Hsp70 is reg ulated at the level of transcription in rainbow trout rbcs, Since trou t rbcs rely heavily on aerobic metabolism, but may also experience ver y low oxygen levels within the circulation, we also examined the relat ive importance of (1) anoxia as a stimulus for Hsp70 synthesis and (2) oxygen as a requirement for protein synthesis under control and heat- shock conditions, We found that trout rbcs were capable of protein syn thesis during 2 h of anoxia, but did not increase Hsp70 synthesis, Mor eover, rbcs subjected to combined anoxia and heat shock exhibited incr eases in Hsp70 synthesis that were similar in magnitude to those in ce lls exposed to heat shock alone, The latter results suggest that rainb ow trout rbcs are (1) able to synthesize non-stress proteins during an oxia, (2) capable of tolerating periods of reduced oxygen availability without increased synthesis of stress proteins and (3) able to mainta in the integrity of their heat-shock response even during periods of a noxia.