Expression of g protein alpha-subunits in bovine parathyroid

A G protein-coupled Ca²⁺-sensing receptor was recently cloned from bovine parathyroid and shown to mediate divalent cation regulation of PTH secretion. To define which G proteins might be coupled to the Ca²⁺-sensing receptor in parathyroid cells, we determined which G protein α-subunit messenger RNAs (mRNAs) are expressed in the parathyroid. We also considered the possibility that a novel parathyroid-specific G α might be present. We, therefore, used the reverse transcription-polymerase chain reaction to study the expression of G α subunits in a bovine parathyroid mRNA preparation. Degenerate primers, corresponding to two regions conserved in every G α subunit, the G3 and G4 sequences, were used to amplify G α complementary DNA fragments that were subcloned and sequenced. We found that mRNAs corresponding to G α s, G α i2, G α 11, G α 12, and G α z are the predominant G α mRNAs expressed in the bovine parathyroid. No novel G α mRNA was identified. Northern blots confirmed the expression of the cloned G α subunits and showed lower expression of G α o and G α i1 mRNAs. Immunoblots confirmed abundant expression of G α s, G α i2, and G α 11 and provided evidence for expression of G α i1 and G α i3, but not G α o. G α q mRNA was not identified by the degenerate primer reverse transcription-polymerase chain reaction strategy, but the immunoblot detected G α q protein, albeit at considerably lower levels than G α 11. The abundance of G α 11 relative to G α q in bovine parathyroid is consistent with but does not prove a role for G α 11 in coupling the Ca²⁺-sensing receptor to phospholipase C.