 loss of G protein- and therefore cell-stimulating ability) after activation by an agonist; TPβ but not TPα undergoes agonist-induced internalization.The expression of α and β isoforms is not equal within or across different cell types.For example, platelets express high concentrations of the α isoform (and possess residual RNA for the β isoform), while expression of the β isoform has not been documented in these cells.