Gross S R, Mayer S E, Longshore M A
J Pharmacol Exp Ther. 1976 Sep;198(3):526-38.
The mechanism by which beta adrenergic agonist stimulate glycogenolysis in intact skeletal muscle was investigated in mice with the phosphorylase kinase deficiency mutation (I strain). Although extracts of I strain diaphragm muscle had only 3.7% of the phosphorylase kinase activity found in extracts of the control strain (C57BL), incubation of I strain hemidiaphragms in Krebs-Ringer bicarbonate buffer with either isoproterenol or epinephrine resulted in a stimulation of the rate of glycogenolysis. In C57BL diaphragms, the EC50 values for isoproterenol and epinephrine were 2 and 14 nM, respectively. With I strain diaphragms, dl-isoproterenol or l-epinephrine stimulated glycogenolysis as a linear function of the log of the drug concentration with no apparent plateau of response up to concentrations of 30 to 40 mugM. For each 10-fold increase in drug concentration, isoproterenol and epinephrine stimulated glycogenolysis in I strain muscles an additional 0.37 to 0.42 mg/g/hr, a slope in the concentration-response relationship of 0.17 and 0.37, respectively, of that measured in C57BL diaphragms at concentrations around the EC50. The highest glycogenolytic response measured in I strain hemidiaphragms (at 40 mugM isoproterenol) was 80% of the maximal catecholamine-stimulated glycogenolysis in C57BL diaphragms. Both 4 nM and 4 mugM isoproterenol, in a concentration-dependent manner, stimulated phosphorylase b to a conversion in I and C57BL diaphragms and increased cyclic adenosine 3':5'-monophosphate (cyclic AMP) concentrations. The glycogenolytic response to 10.1 nM dl-isoproterenol in both I and C57BL diaphragms was blocked by 34 nM l-propranolol but not by 34 nM d-propranolol. The response to 4 mugM isoproterenol was enhanced by the cyclic nucleotide phosphodiesterase inhibitors papaverine (27 mugM) or dl-4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20-1724, 3 mugM). From the results of these studies, we conclude: 1) Catecholamines stimulate glycogenolysis in skeletal muscle of I mice, as in C57BL mice, by interacting with the beta adrenergic receptor, thereby increasing tissue cyclic AMP concentrations and stimulating phosphorylase b to a conversion. 2) alternative hypotheses for the mechanism of the catecholamine-stimulated decrease in glycogen concentration in I skeletal muscle-inhibition of glycogen synthesis, hyposia and 5'-AMP stimulation of phosphorylase b activity-have been ruled out. 3) the activity of the mutant phosphorylase kinase, although it is only 3.7% of that in extracts of C57BL muscle, is sufficient to produce phosphorylase b to a conversion and thereby account for the glycogenolytic response of I strain muscle to catecholamines.
利用磷酸化酶激酶缺陷突变小鼠（I品系）研究了β-肾上腺素能激动剂刺激完整骨骼肌糖原分解的机制。尽管I品系膈肌提取物中的磷酸化酶激酶活性仅为对照品系（C57BL）提取物中的3.7%，但将I品系半膈肌置于含有异丙肾上腺素或肾上腺素的 Krebs-Ringer 碳酸氢盐缓冲液中孵育，会刺激糖原分解速率。在C57BL膈肌中，异丙肾上腺素和肾上腺素的EC50值分别为2 nM和14 nM。对于I品系膈肌，消旋异丙肾上腺素或L-肾上腺素刺激糖原分解呈药物浓度对数的线性函数，在浓度高达30至40 μM时无明显反应平台。药物浓度每增加10倍，异丙肾上腺素和肾上腺素刺激I品系肌肉糖原分解的速率额外增加0.37至0.42 mg/g/hr，浓度-反应关系的斜率分别为在C57BL膈肌EC50浓度附近测得斜率的0.17和0.37。在I品系半膈肌中测得的最高糖原分解反应（在40 μM异丙肾上腺素时）为C57BL膈肌中最大儿茶酚胺刺激糖原分解的80%。4 nM和4 μM异丙肾上腺素均以浓度依赖的方式刺激I品系和C57BL膈肌中的磷酸化酶b转化，并增加环磷腺苷（cAMP）浓度。I品系和C57BL膈肌对10.1 nM消旋异丙肾上腺素的糖原分解反应被34 nM L-普萘洛尔阻断，但不被34 nM D-普萘洛尔阻断。环核苷酸磷酸二酯酶抑制剂罂粟碱（27 μM）或消旋4-(3-丁氧基-4-甲氧基苄基)-2-咪唑啉酮（Ro 20-1724，3 μM）增强了对4 μM异丙肾上腺素的反应。从这些研究结果中，我们得出以下结论：1）儿茶酚胺与β-肾上腺素能受体相互作用，从而增加组织cAMP浓度并刺激磷酸化酶b转化，与在C57BL小鼠中一样，刺激I品系小鼠骨骼肌中的糖原分解。2）儿茶酚胺刺激I品系骨骼肌糖原浓度降低的机制的其他假设——糖原合成抑制、低氧血症以及5'-AMP对磷酸化酶b活性的刺激——已被排除。3）突变型磷酸化酶激酶的活性虽然仅为C57BL肌肉提取物中活性的3.7%，但足以使磷酸化酶b转化，从而解释I品系肌肉对儿茶酚胺的糖原分解反应。
