The hemispheric functional expression of the thyrotropin-releasing-hormone receptor is not determined by the receptors' physical distribution

The thyrotropin-releasing-hormone receptor (TRH-R) is a member of a family of the G-protein-coupled receptors that share structural similarities and exert their physiological action via the inositol lipid signal-transduction pathway. The TRH-R when expressed in Xenopus oocytes exhibits marked preference of the response (increased chloride conductance) for the animal hemisphere. Whereas the rat TRH-R functional distribution was strongly asymmetric (animal/vegetal ratio = 9.5), the mouse TRH-R exhibited a significantly lower ratio (3.9). Truncation of the last 59 amino acids of the C-terminal region of the mouse TRH-R did not lead to any changes in the functional hemispheric distribution. Despite the polarization of response, receptor number was similar on both hemispheres. Moreover, the apparent half-life of the functional expression of the TRH-R was approx. 4 h on both hemispheres when the expression was inhibited by a specific antisense oligonucleotide. Inhibition of total protein synthesis with cycloheximide affected hemispheric responses mediated by each of the three TRH-Rs tested in a qualitatively different way. These results suggest that an additional, rapidly degraded, protein modulates the functional hemispheric expression of the TRH-Rs.