BETA-ADRENOCEPTOR DESENSITIZATION IN SK-N-MC CELLS, A HUMAN CELL-LINECONTAINING A HOMOGENEOUS POPULATION OF BETA(1)-ADRENOCEPTORS

1 Using agonists (adrenaline, noradrenaline, isoprenaline, dopamine, e pinine, procaterol) and antagonists (CGP 20712A and ICI 118,551) in ra dioligand binding and adenylate cyclase-stimulation studies we demonst rate that the human neuroblastoma cell line SK-N-MC contains a homogen eous population of beta1-adrenoceptors coupling to stimulation of aden ylate cyclase. 2 A 24 h treatment with isoprenaline reduced beta1-adre noceptor density, concentration-dependently, maximally by 69 +/- 1%. F unctional beta1-adrenoceptor desensitization was comparatively small. 3 Although 100 nm isoprenaline caused significantly greater receptor d own-regulation than 10 muM isoprenaline (47 +/- 2%), desensitization o f cAMP accumulation in intact cells or of adenylate cyclase stimulatio n in cell membranes was attenuated similarly or even more with 10 muM isoprenaline. 4 While both agonist concentrations did not significantl y alter immunodetectable a-subunits for G(i) or G(o) or G-protein beta -subunits, 10 muM (but not 100 nM) isoprenaline decreased immunodetect able G(salpha). Accordingly, only treatment with 10 muM isoprenaline r educed receptor-independent adenylate cyclase stimulation by GTP, NaF or forskolin. Neither agonist concentration desensitized adenylate cyc lase activation by MnCl2. 5 We conclude that isoprenaline produces a c oncentration-dependent regulation of beta1-adrenoceptor number in SK-N -MC cells, which is weaker at higher than at intermediate agonist conc entrations, and is accompanied by only minor desensitization of adenyl ate cyclase activity; whether this involves alterations of postrecepto r events depends on the agonist concentration used.