Electrophysiological study of the functional structure of the Na channel.

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In this series of experiments using the internal perfusion and the voltage clamp method on squid giant axon, an attempt was made to elucidate the functional structure Na channel by using the newly found biological toxins and chemicals. The experiments were categorized as follows; 1) The mechanism of block of the Na channel from the internal surface of cell membrane by cyclic-polyamine derivatives. cyclam and its analogue having the alkylguanidunium side chain (G-cyclam) have shown to block the Na channel only from the internal surface. Mode of the block is voltage- as well as time-dependent. In the case of G-cyclam, time course of the block is governed by a single exponential function. While, cyclam blocks Na channel with a double exponential function. The enhancement of blocking action occurred when [Na]_i increased from 50 to 200 mM. Two state three barrier model well explains all these blocking actions in the Na channel. from the molecular consideration of these cyclic aolyamine ana … More logues, it is reasonable to assume that alkyl guanidinium group freely moves inside the na channel, thereby attaching the negative charged site and in ture blocking the Na channel. 2) Similar finding also obtained, when two spider toxins, JSTX-3 and NSTX-3, were applied intra-cellularly. These spider toxins have a common 2,4 dihydrooxy-phenylacethyl-aspargynil-cadabelino-ptreamine. Difference in molecular structure is recognized in the terminal where JSTX-3 has gpysine and NSTX-3 arginine residues. Since NSTX-3 exerts stronger blocking action than JSTX-3 does, again freely movable terminal group having a permanent positive charge is assumed to play an important role in blocking the Na channel. 3) Externally applied grayanotoxin (GTX), Na channel modifier, appeared in the intracellu lar phase and induced much bigger depolarization in the non-perfusion of intracellular phase than in the continuous perfusion. Thus, it has been concluded that the site of action is in the intracellular phase. Less