Difference in sensitivity to alkaline phosphatase treatment between rat reticulocyte membranes in which beta-adrenoceptor desensitization was induced by isoproterenol, dibutyryl cAMP and phorbol ester.

The effect of alkaline phosphatase (3.1.3.1) on desensitization of beta-adrenoceptor-responsive adenylate cyclase and the role of phosphorylation in desensitization were examined. Treatment of rat reticulocytes with isoproterenol, dibutyryl cAMP and tetradecanoyl phorbol acetate (TPA) caused the desensitization of beta-adrenoceptor-coupled adenylate cyclase. When the membranes from dibutyryl cAMP- and TPA-desensitized cells were incubated with alkaline phosphatase for 60 min at 30 degrees C, pH 8.0, the desensitization of isoproterenol-stimulated adenylate cyclase was markedly attenuated in both preparations. When the membranes from isoproterenol-desensitized cells were treated with alkaline phosphatase under the same conditions, the attenuation of the desensitization of alkaline phosphatase was less than in the case of treatment with dibutyryl cAMP or TPA. In other words, isoproterenol-induced desensitization was more resistant to alkaline phosphatase treatment. Isoproterenol- and dibutyryl cAMP-induced desensitization of NaF-stimulated adenylate cyclase were also attenuated by alkaline phosphatase treatment. Although the stability of the Gs-catalytic unit complex of adenylate cyclase was reduced by isoproterenol treatment, the reduction of stability was also decreased by alkaline phosphatase treatment.