Hypotension‐induced trafficking of Neurokinin 3 Receptor (NK3‐R) to the nucleus of neurons in the supraoptic nucleus (SON)

Ligand‐induced translocation of the G‐protein‐coupled receptor, NK3‐R, to the nucleus of hypothalamic neurons was reported using antibodies (ABs) raised against the C‐terminal region of NK3‐R. The current work was undertaken to identify which portion of the NK3‐R enters the nucleus. ABs raised against N‐terminal and second extracellular loop regions of rat NK3‐R were used to evaluate western blots of whole cell and nuclear fractions of SON from control and hypotensive rats. CHO cells transfected with rat or human NK3‐R demonstrated specificity of the ABs. The N‐terminal AB prominently recognized a diffuse protein band of ~56–65kD (56kD=predicted size) and a distinct ~70kD protein in whole tissue homogenates while the extracellular loop AB prominently recognized protein of ~95kD in nuclear fractions. Compared to normotensive animals, hydralazine‐induced hypotension significantly increased the density of the ~95kD protein band in nuclear fractions of SON recognized by the extracellular loop AB (t=3.78, p<0.01). This confirms our findings with C‐terminally directed NK3‐R ABs, and demonstrates that a large portion of the NK3‐R translocates to the nucleus in response to a physiological stimulus for vasopressin release. Nuclear NK3‐R may participate in regulation of gene expression in vasopressin neurons. Supported by NIH grants R21‐NS059569 to CDS and RO1‐NS57823 and P20‐RR15640 to FWF.