ABSTRACT
The renal medulla is the only mammalian tissue normally exposed to elevated total osmolality as a consequence of the renal concentrating mechanism. NaCl and urea contribute the bulk of this excess osmolality. The immediate-early genes comprise a diverse group of genes that can be rapidly and transiently upregulated at the messenger RNA level in response to a particular stimulus, even in the absence of new protein synthesis. The heat shock response is an extremely highly conserved genetic program inducible by a variety of chemical and physical stimuli, including heat shock, oxidative stress, and heavy metals. A potential role for members of the HSP70 family in adaptation to hyperosmotic stress can readily be envisioned from their reputed role in governing the assumption and maintenance of protein conformation. Assumption of intracellular volume regulation with nonperturbing or even counteracting osmolytes, as well as the presence of protein-stabilizing chaperonins together ameliorate the alteration in intracellular protein conformation and provide a negative feedback loop.
