Xiao R P, Hohl C, Altschuld R, Jones L, Livingston B, Ziman B, Tantini B, Lakatta E G
Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224.
J Biol Chem. 1994 Jul 22;269(29):19151-6.
Previous studies have shown that both beta 1- and beta 2-adrenergic receptors (AR) are present in rat ventricular myocytes, but stimulation of these receptor subtypes elicits qualitatively different cellular responses (Xiao, R.-P., and Lakatta, E. G. (1993) Circ. Res. 73, 286-300). In the present study, the biochemical mechanism underlying the distinct beta AR subtype actions have been investigated. Although both beta 1AR and beta 2AR stimulation increased total cellular cAMP in suspensions of rat ventricular myocytes to a similar extent, the maximum elevation of the membrane bound cAMP by beta 2AR stimulation was only half of that induced by beta 1AR stimulation, suggesting that stimulation the beta AR subtypes leads to different compartmentation of cAMP. The effects of beta 1AR stimulation on Ca2+ transient (indexed by the transient increase in indo-1 fluorescence ration after excitation) and contraction amplitude (measured via photodiode array) and their kinetics closely paralleled the increase in cAMP. In contrast, the increase in both membrane bound and total cAMP content after beta 2AR stimulation were completely dissociated from the effects of beta 2AR stimulation to increase the amplitudes of cytosolic Ca2+ transient and contraction. Furthermore, beta 2AR stimulation did not phosphorylate phospholamban to the same extent as did beta 1AR stimulation. This finding provides a mechanism for the failure of beta 2AR stimulation to accelerate the kinetics of the Ca2+i (cytosolic Ca2+) transient and contraction. These results indicate that the effects of beta 2AR stimulation on Ca2+i transient and contraction are uncoupled from the cAMP production and cAMP-dependent protein phosphorylation and indicate that, in addition to coupling to adenylate cyclase, beta 2AR stimulation also activates other signal transduction pathway(s) to produce changes in cytosolic Ca2+ and contraction.
以往的研究表明，β1 - 和β2 - 肾上腺素能受体（AR）均存在于大鼠心室肌细胞中，但刺激这些受体亚型会引发性质不同的细胞反应（Xiao，R.-P.，和Lakatta，E.G.（1993年）《循环研究》73卷，286 - 300页）。在本研究中，对不同β肾上腺素能受体亚型作用背后的生化机制进行了研究。尽管刺激β1AR和β2AR均使大鼠心室肌细胞悬液中的总细胞内环磷酸腺苷（cAMP）增加到相似程度，但β2AR刺激引起的膜结合cAMP的最大升高仅为β1AR刺激诱导值的一半，这表明刺激β肾上腺素能受体亚型会导致cAMP的不同区室化。β1AR刺激对Ca2 + 瞬变（通过激发后indo - 1荧光比率的瞬时增加来衡量）、收缩幅度（通过光电二极管阵列测量）及其动力学的影响与cAMP的增加密切平行。相比之下，β2AR刺激后膜结合和总cAMP含量的增加与β2AR刺激增加胞质Ca2 + 瞬变和收缩幅度的效应完全分离。此外，β2AR刺激对受磷蛋白的磷酸化程度不如β1AR刺激。这一发现为β2AR刺激未能加速胞质Ca2 + （Ca2 + i）瞬变和收缩的动力学提供了一种机制。这些结果表明，β2AR刺激对Ca2 + i瞬变和收缩的影响与cAMP产生及cAMP依赖性蛋白磷酸化解偶联，并且表明，除了与腺苷酸环化酶偶联外，β2AR刺激还激活其他信号转导途径以产生胞质Ca2 + 和收缩的变化。
