| Abstract: | HeLa cells contain receptors on their surface which are beta-adrenergic in nature. The binding of (-)-3H]dihydroalprenolol is rapid, reversible, stereospecific and of relatively high affinity. The HeLa cells also contain an adenylate cyclase which is activated by (-)-isoproterenol greater than (-)-epinephrine greater than (-)-norepinephrine. The adenylate cyclase of HeLa is also activated by guanyl-5'-ylimidodophosphate (Gpp(NH)p), a nonhydrolyzable analogue of GTP. Inclusion of both (-)-isoproterenol and Gpp(NH)p leads to approximately additive rather than synergistic activation of adenylate cyclase. After treatment of HeLa cells with 5mM sodium butyrate there is an increase in the number of beta-adrenergic receptors, but not in their affinity, which is reflected in an increased ability of (-)-isoproterenol to activate adenylate cyclase. Other properties of the beta-adrenergic receptor including association and dissociation rates, temperature optimum of adenylate cyclase and response to Gpp(NH)p are relatively unaffected by butyrate pretreatment of the cells. |
