[Specific expression and distribution of the isoforms of GTP binding protein beta subunits in hearts]

A growing body of evidence now supports the idea that free beta gamma subunits of GTP binding proteins (G proteins) can themselves interact functionally with effector proteins. Recent results suggest that beta subunits might be playing a key role to specify the receptor-effector coupling in various transmembrane signaling systems. The purpose of this study is to examine the expression level and distribution of G protein beta subunits in rat hearts. Brain and ventricle of WKY rats were used to examined the expression of three different isoforms of beta subunits in mRNA and protein level by means of Northern blot and Western blot analysis, respectively. beta 3 mRNA was expressed significantly more in ventricles than in brains. This result was supported by Western blot analysis showing that beta 3 was expressed more in ventricles. For all three isoforms (beta 1 beta 2 and beta 3), the majority of beta subunits expressed in rat hearts were detected in cytosolic fractions. An ultrafiltration and subsequent Western blot analysis revealed that the beta subunits in ventricular cytosolic fractions had molecular mass greater than 100,000 dalton. In this study, tissue-specific expression of beta subunit isoforms was revealed in rat hearts.