科研之友
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摘要
beta(3)-Adrenoceptors are resistant to agonist-induced desensitization in some cell types but susceptible in others including transfected human embryonic kidney (HEK) cells. Therefore, we have studied cellular and molecular changes involved in agonist-induced beta(3)-adrenoceptor desensitization in HEK cells. Cells were treated with isoprenaline or forskolin, and following wash-out, cyclic adenosine monophosphate (cAMP) accumulation in response to freshly added agonist was quantified. Receptor and G protein expression were quantified by radioligand binding and immunoblot experiments, respectively. Treatment with isoprenaline induced a concentration- and time-dependent desensitization of cAMP accumulation in response to freshly added isoprenaline. This functional desensitization primarily consisted of reduced maximum responses with little change of agonist potency. Maximum desensitization was achieved by pre-treatment with 10 mu M isoprenaline for 24 h. It was not accompanied by changes in beta(3)-adrenoceptor density as assessed in saturation radioligand-binding studies. The desensitization was associated with a small reduction in immunoreactivity for alpha-subunits for G(s) and G(i1), whereas that for G(i2), G(i3), and G(q/11) was not significantly altered. In cells treated with pertussis toxin, isoprenaline-induced cAMP accumulation as well as desensitization by isoprenaline pre-treatment remained unchanged. Isoprenaline pre-treatment also reduced forskolin-induced cAMP accumulation; conversely, pre-treatment with forskolin caused a similar desensitization of isoprenaline-induced cAMP accumulation. We conclude that agonist-induced beta(3)-adrenoceptor desensitization in HEK cells does not involve reduced receptor numbers and small, if any, reduction of G(s) expression; changes at the level of adenylyl cyclase function can fully explain this desensitization.
- 出版日期2013-10
