Interaction of n-alkylguanidines with the sodium channels of squid axon membrane.

Abstract

A BST RA CT The effects of n-alkylguanidine derivatives on sodium channel conductance were measured in voltage clamped, internally perfused squid giant axons. After destruction of the sodium inactivation mechanism by internal pronase treatment, internal application of n-amylguanidine (0.5 mM) or noctylguanidine (0.03 raM) caused a time-dependent block of sodium channels. No time-dependent block was observed with shorter chain derivatives. No change in the rising phase of sodium current was seen and the block of steadystate sodium current was independent of the membrane potential. In axons with intact sodium inactivation, an apparent facilitation of inactivation was observed after application of either n-amylguanidine or n-octylguanidine. These results can be explained by a model in which alkylguanidines enter and occlude open sodium channels from inside the membrane with voltage-independent rate constants. Alkylguanidine block bears a close resemblance to natural sodium inactivation. This might be explained by the fact that alkylguanidines are related to arginine, which has a guanidino group and is thought to be an essential amino acid in the molecular mechanism of sodium inactivation. A strong correlation between alkyl chain length and blocking potency was found, suggesting that a hydrophobic binding site exists near the inner mouth of the sodium channel.

Removal of sodium channel inactivation in squid axon by the oxidant chloramine-T.

“…Cleavage alone, however, only indicates the presence, and not the functional importance, of these residues . Subsequent experiments with lysineand arginine-modifying reagents and with agents that mimic peptides containing arginine Kirsch et al, 1980;Lo and Shrager, 1982;Nonner et al, 1980) have demonstrated that an arginine residue was probably present and was an integral part of the inactivation mechanism.…”

Accelerating effects of pentobarbitone on the inactivation process of the calcium current in Helix neurones

“…Pancuronium (Yeh & Narahashi, 1977), N-alkylguanidines (Kirsch, Yeh, Farley & Narahashi, 1980) and gallamine (Smith & Schauf, 1981) are known to block the open-state of the voltagedependent sodium channel, resulting in acceleration of the decay of sodium current without affecting the rising phase of the current. As to calcium current (ICa), the inactivation process (the decay phase of ICa) has been analysed in various tissues, and ICa after reaching its peak, is inactivated in a voltage-and current-dependent manner (Kostyuk, Krishtal & Shakhovalov, 1977;Akaike, Lee & Brown, 1978;Brehm & Eckert, 1978;Tillotson, 1979;Brown, Morimoto, Tsuda & Wilson, 1981;Plant & Standen, 1981).…”

Guanidinium analogues as probes of the squid axon sodium pore. Evidence for internal surface charges.

“…The block of sodium channel currents by guanidinium compounds is time dependent (Morello et al, 1980;Kirsch et al, 1980). Consequently, we estimated steady state block using currents measured at the end of 4-ms voltage-clamp pulses.…”

“…However, the results of several studies have implicated the involvement of the amino acid arginine on the internal side of the membrane in the inactivation process (Rojas and Rudy, 1976;Eaton et al, 1978;Brodwick and Eaton, 1978). Since arginine contains a guanidinium group, several laboratories have investigated the actions of internal guanidinium analogues on sodium channel function (Morello et al, 1980;Kirsch et al, 1980;Lo and Shrager, 1981a, b). Internally applied monovalent and divalent guanidinium analogues inhibit sodium channel current.…”