A Novel Mechanism For Long QT Syndrome Mutations In KCNQ1 Gene And The Effects Of Ethanol On KCNQ1 Channel

Ion channels are protein pores of cellular membranes and ion flow is the basis of signal transfer between different cells. Potassium channel is a popular branch of membrane protein, and plays very important roles in many physiological activities. KCNQ gene is one of the genes encoding voltage-dependent potassium channels. If mutations existed in KCNQ gene, serious "ion channel disease"will be resulted. Long QT syndrome (LQTS) is the main representation of them. KCNQ1 gene and the protein coded by it were introduced from the aspects of structure, physiology, and electrophysiology. The hot points and the main conclusions of researches about KCNQ1 were also summed up. The relationship between KCNQ1 mutations and disease, as well as the pathophysiologic and pharmacological research related, were introduced in detail. To understand the underlying genetic basis of Chinese families with Long QT syndrome, the causally related genes were screened and the functional consequences of the identified gene mutations were evaluated in vitro using double-electrode voltage clamp technique. In this study, two missense mutants, L191P and F275S, in the KCNQ1 gene from the Chinese families with long QT syndrome, were under electrophysiological validation. Compared with wild-type KCNQ1/KCNE1 channels, co-expression of L191P-KCNQ1 or F275S-KCNQ1 with KCNE1 in Xenopus oocytes reduced the wild-type KCNQ1 current (or IKs current) by more than 70%. The GV curves of both mutations shifted about 20⁴0 mV to the positive direction and the time constants of both the activation and the deactivation were reduced. The mutant F275S/minK displayed an inactivation of KCNQ1 currents. Co-expression of wild type KCNQ1 and its mutations with 1:1 ratio brought a dominant-negative effect on I_Ks currents. Here we also found that both the mutant L191P-KCNQ1 and F275S-KCNQ1 resulted in the diminishment of the single conductance and the dominant-negative effect of I_Ks currents through the interaction with KCNE1 instead of the inactivation of F275S-KCNQ1. This may underlie the molecular mechanism of ventricular arrhythmias and sudden death in the Chinese Long QT patients. In addition, we studied the effects of ethanol on the delayed rectified K+ currents (IKs) coded by KCNQ1 and KCNE1 in Xenopus oocytes from many aspects of currents'properties. Ethanol blocked IKs in a concentration-dependent manner at the range of 20～500 mmol/L, with an IC50 value of 137.3±6.39 mmol/L. Besides, the blockade occured rapidly, with a steady level achieved in 2 minutes after the replacement of bath solution by ethanol. Steady-state activation curve was also shifted to the right when ethanol was used, which suggested that the gating properties of the potassium channels were altered. We hold the opinion that ethanol interacts directly with a hydrophobic domain of the channel protein to exhibit its effects. Our results provide information to illuminate the mechanism of the regulations of ethanol on ventricular cells from the aspect of potassium channels.