Molecular and Applied Pharmacology of Subunits of Ion Channels as Biosensors

利用非洲爪蟾卵母细胞中表达的均匀通道群体，研究了1个、2个或4个灭活球对大鼠Kv1.4通道n型灭活的影响。构建了Kv1.4的串联二聚体和四聚体结构体。串联cdna Kv1.4-Kv1.4 delta1 -145和Kv1.4-[Kv1.4 delta1 -145](3)编码的通道分别具有两个或只有一个系留失活球，而Kv1.4本身编码的通道具有四个失活球。随着失活球数的减少，宏观电流失活时间常数显著增加，而失活恢复时间常数没有变化。Kv1.4-Kv1.4 delta1 -145和Kv1.4-[Kv1.4 delta1 -145](3)通道的失活速率常数（k (inact)）与Kv1.4通道的失活速率常数（k (rec)）之比分别为0.65和0.4，而这些通道的恢复速率常数（k (rec)）与Kv1.4通道的速率常数之比几乎一致。具有两个和四个失活球的通道的速率常数k（更准确）比每个通道上的失活球是独立的情况下的速率常数k要小，这表明失活球之间发生了一些相互作用。此外，当通道上失活球的数量减少时，非失活电流变得明显。电压依赖性钙通道对钙内流和平滑肌收缩至关重要。已知这些通道的β亚基通过形成孔隙的alfa1亚基来修饰钙电流。在四个已报道的独立β亚基中，我们分析了心血管系统中的β a3亚基。电生理检查证实平滑肌细胞中存在二氢吡啶敏感的l型钙通道。β a3缺失小鼠在正常饮食中平滑肌收缩和对DHP的敏感性没有明显变化，血压正常，但β a3亚基缺失小鼠在高盐饮食中表现出血压升高，血浆儿茶酚胺浓度显著降低。我们的发现强烈表明，钙通道β亚基零突变的适应导致盐敏感性高血压。少

N-type inactivation of rat Kv1.4 channels with one, two, or four inactivation balls was investigated using homogeneous populations of channels expressed in Xenopus oocytes. Tandem dimeric and tetrameric constructs of Kv1.4 were made. Channels encoded by tandem cDNAs Kv1.4-Kv1.4Delta1-145 and Kv1.4-[Kv1.4Delta1-145] (3) have two or only one tethered inactivation ball, respectively, whereas Kv1.4 itself encodes channels having four inactivation balls. The time constants for inactivation of macroscopic currents were increased significantly as the number of inactivation balls was decreased, whereas the time constants for recovery from inactivation were not modified. The ratios of the rate constants of inactivation (k (inact) ) of Kv1.4-Kv1.4Delta1-145 and Kv1.4-[Kv1.4Delta1-145] (3) channels to that of the Kv1.4 channel were 0.65 and 0.4, respectively, whereas the ratios of the rate constant of recovery (k (rec) ) of these channels to that of Kv1.4 were almost unity. The rate constants k ( … More inact) for channels having two and four inactivation balls are smaller than those that would be expected if inactivation balls on each channel are independent, suggesting some interaction occurs between inactivation balls. Furthermore, noninactivating current became apparent as the number of inactivation balls on a channel was decreased.Voltage-dependent calcium channels are crucially important for calcitum influx and following smooth muscle contraction. Beta subunits of these channels are known to modify calcium currerns through pore-forming alfa1 subunits. Among four reported independent beta subunit, the beta3 subunit in cardiovascular system, we have analyzed beta3-null mice. Electrophysiological examinations proved the existence of dihydropyridine (DHP)-sensitive, L-type calcium channels in the smooth muscle cell. Beta3-null mice show no apparent changes in smooth muscle contraction and sensitivity to DHP, and normal blood pressure when they are raised on a normal diet, but the beta3 subunit deficient mice show elevated blood pressure in response to a high-salt diet, with significant reductions in plasma catecholamine concentration. Our finding strongly suggests the adaptation to the null mutation of calcium channel beta subunit results in salt-sensitive hypertension. Less