THE SHORT AND LONG FORMS OF THE ALPHA-SUBUNIT OF THE STIMULATORY GUANINE-NUCLEOTIDE-BINDING PROTEIN ARE UNEQUALLY REDISTRIBUTED DURING (-)-ISOPROTERENOL-MEDIATED DESENSITIZATION OF INTACT S49 LYMPHOMA-CELLS

We report here that desensitization of the beta-adrenergic receptor-tr iggered transmembrane signalling in S49 wild-type lymphoma cells, indu ced by (-)-isoproterenol (1 mu M), results in unequal intracellular re distribution of the splicing variants of the a subunit of the stimulat ory guanine-nucleotide-binding regulatory (G(s alpha)) protein (G(s al pha-short) and G(s alpha-long)) and alters the functional characterist ics of the membrane-associated signal. transduction complex. We found that two cellular pools of membranes, light-density membranes and plas ma membranes prepared by sucrose-density-gradient centrifugation of ce ll homogenates differed in their content of G(s alpha) splicing subfor ms and, moreover, that prolonged activation of the beta-adrenergic pat hway induced intermembrane redistribution of the splicing variants of G(s alpha). Short (10 min) as well as prolonged (1 h) (-)-isoprotereno l treatment of the cells shifted G(s alpha-short) from light-density m embranes to plasma membranes and increased the total amount of light-d ensity membrane-bound G(s alpha-long) in parallel, the maximal (-)-iso proterenol-stimulated or AlF4--stimulated adenylyl cyclase activities measured in the plasma membrane pools prepared from treated cells decr eased. The functional characteristics of the membrane-bound G(s alpha) pools were examined by a cyc(-)-reconstitutive adenylyl cyclase assay where extracts of the plasma membrane and light-density-membrane pool s, respectively, were mixed with plasma membranes derived from the mut ant S49 cell line, cyc(-), lacking G(s alpha). The maximal cyc(-)-reco nstitutive activities of the extracts prepared from light-density memb ranes of short-term as well as long-term desensitized cells increased compared to control cells. These findings may indicate differences in the functioning of the splicing variants of G(s alpha).