Hypertonicity induced modulation of gene transcription and translation of water regulatory molecules

The cells in the renal medulla are exposed to very high osmolality which may exceed 3000 mosmol/kg water depending on the hydration status of the animal. This osmotic stress caus-es numerous perturbations because of the hypertonic effects of high NaCl and the direct de-naturation of cellular molecules by high urea. High NaCl and urea result in increase of reac-tive oxygen species, inhibit DNA replication and transcription. Adaptive responses and sub-sequent modulation result in changes of gene transcription and translation of water regula-tory biomolecules like the vasopressin, aquaporin, atrial natriuretic peptide and urocortin. For e.g urocortin mRNA in the supraoptic nucleus has been shown to be increased in both vasopressin and oxytocin magnocellular cells after chronic salt loading. On the other hand the increase of AQP2 expression in response to extracellular hypertonicity is independent of the cAMP-PKA pathway. The tonicity responsive enhancer binding protein, TonEBP is ac-tivated and leads to the adaptive responses and causes transcriptional and translational modifications of several water regulatory molecules mentioned above