We have previously reported the relative mRNA and protein level of the long and short splice variants of Gs alpha (Gs alpha L and Gs alpha S) in human atrium. We have now measured the relative proportions of the serine+ and serine- variants of Gs alpha L and Gs alpha S in human atrium, and assessed, indirectly, whether their differential expression may (i) regulate Gs alpha phosphorylation, and (ii) be regulated by atrial cyclic AMP levels. 2. The serine+ and serine- variants of Gs alpha L and Gs alpha S were estimated by single nucleotide primer extension in 36 right atrial strips of which half were from beta-adrenoceptor-blocked patients. The ratio of serine+ to serine- variants was 0.06 +/- 0.12 for Gs alpha L, compared with 8.04 +/- 12.16 for Gs alpha S (P < 0.001). 3. Isoelectric points of Gs alpha and Gs alpha S in the atria of four beta-adrenoceptor-blocked and four non-beta-adrenoceptor-blocked patients were estimated by two-dimensional gel electrophoresis. Two-dimensional gel analysis gave a consistent pattern with several spots for both Gs alpha L and Gs alpha S; however, the isoelectric points of Gs alpha S were more acid (5.18 +/- 0.24) than those of Gs alpha L (5.87 +/- 0.17, P < 0.001). 4. No significant difference in either the serine variants or isoelectric point value was observed between beta-adrenoceptor-blocked and non-beta-adrenoceptor-blocked patients. 5. In conclusion, all four Gs alpha variants were expressed in human atrium, but Gs alpha L is almost entirely of the serine- form. Gs alpha S has a more acidic isoelectric point than Gs alpha L, indicating a possible post-translational modification. The lack of difference in our results between beta-adrenoceptor-blocked and non-beta-adrenoceptor-blocked patients suggests indirectly that cyclic AMP is an unlikely candidate for regulating splicing or post-translational modification of Gs alpha in vivo.
