The beta-subunit has marked effects on the biophysical and pharmacological properties of voltage-dependent calcium channels. In the present study we examined the ability of the GABAB agonist (-) -baclofen to inhibit calcium channel currents in cultured rat dorsal root ganglion neurones following depletion of beta-subunit immunoreactivity, 108-116 h after microinjection of a beta-subunit antisense oligonucleotide. 2.We observed that, although the calcium channel current was markedly reduced in amplitude following beta-subunit depletion, the residual current (comprising both N- and L-type calcium channel currents) showed an enhanced response to application of (-) -baclofen. Therefore, it is possible that there is normally competition between activated G protein G(o) and the calcium channel beta-subunit for binding to the calcium channel alpha 1-subunit; and this competition shifts in favour of the binding of activated G(o) following depletion of the beta-subunit, resulting in increased inhibition. 3. This hypothesis is supported by evidence that an antibody against the calcium channel beta-subunit completely abolishes stimulation of the GTPase activity of G(o) by the dihydropyridine agonist S-(-) -Bay K 8644 in brain membranes. This stimulation of GTPase is thought to result from an interaction of G(o) alpha-subunit (G alpha o) with its calcium channel effector which may operate as a GTPase-activating protein. 4. These data suggest that the calcium channel beta-subunit when complexed with the beta 1-subunit normally inhibits its association with activated G(o). It may function as a GTPase-activating protein to reduce the ability of activated G(o) to associate with the calcium channel, and thus limit the efficacy of agonists such as (-) -baclofen.
摘要
β亚基对电压依赖性钙通道的生物物理和药理学特性具有显著影响。在本研究中，我们在显微注射β亚基反义寡核苷酸108 - 116小时后，β亚基免疫反应性耗尽的情况下，检测了GABAB激动剂(-)-巴氯芬抑制培养的大鼠背根神经节神经元中钙通道电流的能力。2. 我们观察到，虽然β亚基耗尽后钙通道电流幅度明显降低，但残余电流（包括N型和L型钙通道电流）对(-)-巴氯芬的应用表现出增强的反应。因此，正常情况下，活化的G蛋白G(o)与钙通道β亚基之间可能存在竞争，以结合钙通道α1亚基；β亚基耗尽后，这种竞争有利于活化的G(o)结合，导致抑制作用增强。3. 这一假设得到了以下证据的支持：针对钙通道β亚基的抗体完全消除了二氢吡啶激动剂S-(-)-Bay K 8644对脑膜中G(o)的GTP酶活性的刺激。这种GTP酶的刺激被认为是由于G(o)α亚基（Gαo）与其钙通道效应器相互作用所致，该效应器可能作为一种GTP酶激活蛋白发挥作用。4. 这些数据表明，钙通道β亚基与β1亚基复合时，通常会抑制其与活化的G(o)的结合。它可能作为一种GTP酶激活蛋白，降低活化的G(o)与钙通道结合的能力，从而限制(-)-巴氯芬等激动剂的效力。
