Xia Y, Haddad G G
Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510.
J Comp Neurol. 1991 Dec 8;314(2):278-89. doi: 10.1002/cne.903140206.
Our previous results have shown that KATP channels play an important role in K+ efflux and extracellular K+ accumulation in the rat brain, and this role was quantitatively more important in the adult than in the newborn brain. The purpose of this study was to localize by autoradiographic techniques the binding sites of glibenclamide, a potent sulfonylurea ligand that targets KATP channels, in the adult and newborn rat central nervous system (CNS). Since the adult turtle is resistant to anoxia, we also compared the rat to the turtle brain sulfonylurea receptor distribution. In all three animal groups (newborn rat, adult rat, adult turtle), specific glibenclamide binding was saturable. Scatchard plots were curvilinear in the rat, thus suggesting that glibenclamide binds to two types of sites, i.e., high and low affinity sites. Scatchard analysis on turtle brain tissue showed evidence of one binding site only. We also found that the distribution of glibenclamide binding sites was heterogeneous in the adult rat CNS with a higher density in rostral than in caudal regions. The highest binding densities were seen in the cortex, hippocampus, cerebellum, substantia nigra, and a few thalamic nuclei; intermediate densities were observed in the basal ganglia, septum, thalamus, and the hypoglossal nucleus. There was a low density in most areas of the hypothalamus, midbrain, brainstem, and spinal cord. Compared with the adult rat, the newborn had a very homogeneous distribution of binding sites and densities were very low throughout the CNS; the level of binding density was even lower in some regions undetectable in the adult turtle. Our results indicate that (1) there are high and low affinity sulfonylurea receptors in the rat CNS, (2) there is a striking heterogeneity in the distribution and density of sulfonylurea receptors in the adult rat CNS and this is in sharp contrast to the homogeneous distribution and low density in both newborn rat and adult turtle; (3) sulfonylurea receptors increase in number postnatally in the rat since binding density increases and the Kd in the newborn rat is similar to that in the adult rat. We speculate that KATP channels and sulfonylurea receptors are poorly developed in the turtle and develop mostly after birth in the rat, reaching highest density in adulthood.
我们之前的研究结果表明，KATP通道在大鼠脑内钾离子外流及细胞外钾离子蓄积过程中发挥重要作用，且该作用在成年大鼠脑中比在新生大鼠脑中更为重要。本研究旨在采用放射自显影技术定位强效磺脲类配体格列本脲（一种作用于KATP通道的物质）在成年及新生大鼠中枢神经系统（CNS）中的结合位点。由于成年海龟对缺氧具有耐受性，我们还比较了大鼠与海龟脑内磺脲类受体的分布情况。在所有三组动物（新生大鼠、成年大鼠、成年海龟）中，格列本脲的特异性结合均具有饱和性。大鼠的Scatchard图呈曲线状，这表明格列本脲与两种类型的位点结合，即高亲和力位点和低亲和力位点。对海龟脑组织进行的Scatchard分析仅显示存在一个结合位点。我们还发现，成年大鼠CNS中格列本脲结合位点的分布不均一，吻侧区域的密度高于尾侧区域。结合密度最高的部位见于皮质、海马、小脑、黑质及少数丘脑核团；基底神经节、隔区、丘脑及舌下神经核的密度中等。下丘脑、中脑、脑干及脊髓的大部分区域密度较低。与成年大鼠相比，新生大鼠的结合位点分布非常均一，且整个CNS中的密度都很低；在成年海龟中无法检测到的某些区域，新生大鼠的结合密度水平甚至更低。我们的结果表明：（1）大鼠CNS中存在高亲和力和低亲和力的磺脲类受体；（2）成年大鼠CNS中磺脲类受体的分布和密度存在显著的不均一性，这与新生大鼠和成年海龟中均一的分布及低密度形成鲜明对比；（3）由于结合密度增加且新生大鼠的解离常数（Kd）与成年大鼠相似，大鼠出生后磺脲类受体数量增加。我们推测，海龟体内的KATP通道和磺脲类受体发育不完善，而在大鼠中主要在出生后发育，成年时达到最高密度。
