Possible screening of surface charges on crayfish axons by polyvalent metal ions

Abstract

SUMMARY1. The effect of different polyvalent metal ions in the external solution upon the threshold membrane potential for spike initiation in crayfish axons has been studied by means of intracellular micro-electrodes. The metal ions tested included six divalent cations (Ca2+, Mg2+, Sr2+, Ba2+, Co2+, and Ni2+) and three trivalent cations (La +, Y3+ and Eu3+).2. Identical extracellular concentrations of different cations with the same valence had essentially the same effect on threshold membrane potential. However, a very low concentration of trivalent cations (about 225 /SM) was found to be equivalent to a much higher divalent cation concentration (13.5 mM) as measured by their effects on threshold potential.3. Upon a tenfold increase in concentration, the threshold potential for spike initiation was shifted in a positive direction by 30-6 mV with divalent cations and by 208 mV with trivalent cations.4. It is shown that a hypothesis involving screening of negative charges at the axonal membrane surface, based on Gouy-Chapman theory, predicts these various experimental results rather closely.5. It is concluded that a high negative charge density, sufficient to render a screening mechanism possible, exists at the surface of crayfish axons in the region of the sodium 'gates'. 6. The density of surface charges is calculated to be approximately le-/43 A2. This calculation is discussed in connexion with the possible molecular identity of the sodium 'gates' in crayfish axons and other excitable systems.

Comparison of the action of La3+ and Ca2+ on contraction threshold and other membrane parameters of frog skeletal muscle

“…The threshold of the action potential was shifted to less negative values. This finding agrees with the results on crayfish axon given by D'Arrigo (1973).…”

“…The trivalent rare earth alkaline cation lanthanum has been shown to affect ion permeabilities in nerve and the activation of contraction in skeletal muscle in a similar way as calcium (Takata et al, 1966;Blaustein & Goldman, 1968;D'Arrigo, 1973;Hartz & Ulbricht, 1973;Andersson & Edman, 1974b;D6rrscheidt-Kiifer & Ltittgau, 1974;Vogel, 1974). These authors reported a shift in sodium and potassium permeability curves to less negative potentials in a variety of nerve preparations at relatively low [La3+l o (<1 raM), and an eventual block of action potential conductance after longer application or at concentrations of ca.…”

Long-lasting inward current in snail neurons in barium solutions in voltage-clamp conditions

“…The explanation for this effect may be that Ba, having nearly the same crystal or singly hydrated radius as K, may plug K § channels in the membrane (Mullins, 1961;Werman & Grundfest, 1961;Sperelakis & Lehmkuhl, 1966;Krnjevic, Pumain & Renaud, 1971). The effect of Ba on some axons appears to be very similar to that of Ca (Narahashi, 1966;Blaustein & Goldman, 1968;D'Arrigo, 1973). Fatt and Ginsborg (1958), Hagiwara and Naka (1964), and Hagiwara, Fukuda and Eaton (1974) regard Ba as an efficient carrier of the inward current through the Ca channel in crustacean muscle fibers.…”

Microelectrode studies of the effect of lanthanum on the electrical potential and resistance of outer and inner cell membranes of isolated frog skin

“…5b We started on the basis of the hypothesis that surface potential affects the conductance of the outer border sodium channel (Grinstein et al, 1978;Goudeau et al, 1979). If such a negative surface potential (Naharashi, 1966;Ito, Kuriyama & Tashiro, 1970;D'Arrigo, 1973) is reduced by La 3+ on the outer side of the membrane, this leads to an increase in the intramembrane inward electrical field. In view of the above evidence of the voltage dependency of the apical border sodium conductance (with an increased conductance when the cell hyperpolarizes) such a La 3 +-induced rise in the electrical field could produce the observed sodium conductance increase.…”