Calcium ions affect the gating of Ca currents. Surface charge is involved
but to what extent is unknown. We have examined this, using isolated
nerve cell bodies of Helix aspersa and the combined microelectrode-suction
pipette method for voltage-clamp and internal perfusion. We found
that Ba and Sr currents produced by substitution of these ions for
extracellular Ca ions are activated at less positive potentials than
Ca currents. Mg ions do not permeate the Ca channel and changes in
Mgo produce shifts in the activation-potential curves that are
comparable to the effects of changes in Bao or Sro. Inactivation
of Ba currents also occurs at less positive potentials. Perfusion
intracellularly with EGTA reduced inactivation of Ca currents as
a function of potential, but did not shift the inactivation-potential
curve. Hence, Ca current-dependent inactivation which is blocked
by intracellular EGTA probably does not involve a similar change
of intracellular surface potential. The voltage shifts of activation
and inactivation produced by extracellular divalent cations used
singly or in mixtures can be described by the Gouy-Chapman theory
for the diffuse double layer with binding (Gilbert & Ehrenstein,
1969; McLaughlin, Szabo & Eisenman, 1971). From the surface potential
values and the Boltzman distribution, we have computed surface concentrations
that predict the following experimental observations: 1) saturation
of current-concentration relationships when surface potential is
changing maximally; 2) the increase in peak current when Ca ions
are replaced by Sr or Ba ions; and 3) the greater inhibitory effect
of Mg on IBa than ICa. Theory indicates that surface charge cannot
be screened completely even at 1 M Mgo and thus that Ca channel
properties must be evaluated in the light of surface charge effects.
For example, after correction for surface charge effects the relative
permeabilities of Ca, Ba and Sr ions are equivalent. In the presence
of Co ions, however, Ca ions are more permeable than Ba ions suggesting
a channel binding site may be involved.
%0 Journal Article
%1 Wils_1983_117
%A Wilson, D. L.
%A Morimoto, K.
%A Tsuda, Y.
%A Brown, A. M.
%D 1983
%J J. Membr. Biol.
%K (Snails), 6304316 Active, Animals, Biological Biotransformation, Calcium, Channels, Gov't, Helix In Ion Magnesium, Membrane Neurons, P.H.S., Potentials, Properties, Research Support, Surface Transport, U.S. Vitro,
%N 1-2
%P 117--130
%T Interaction between calcium ions and surface charge as it relates
to calcium currents.
%V 72
%X Calcium ions affect the gating of Ca currents. Surface charge is involved
but to what extent is unknown. We have examined this, using isolated
nerve cell bodies of Helix aspersa and the combined microelectrode-suction
pipette method for voltage-clamp and internal perfusion. We found
that Ba and Sr currents produced by substitution of these ions for
extracellular Ca ions are activated at less positive potentials than
Ca currents. Mg ions do not permeate the Ca channel and changes in
Mgo produce shifts in the activation-potential curves that are
comparable to the effects of changes in Bao or Sro. Inactivation
of Ba currents also occurs at less positive potentials. Perfusion
intracellularly with EGTA reduced inactivation of Ca currents as
a function of potential, but did not shift the inactivation-potential
curve. Hence, Ca current-dependent inactivation which is blocked
by intracellular EGTA probably does not involve a similar change
of intracellular surface potential. The voltage shifts of activation
and inactivation produced by extracellular divalent cations used
singly or in mixtures can be described by the Gouy-Chapman theory
for the diffuse double layer with binding (Gilbert & Ehrenstein,
1969; McLaughlin, Szabo & Eisenman, 1971). From the surface potential
values and the Boltzman distribution, we have computed surface concentrations
that predict the following experimental observations: 1) saturation
of current-concentration relationships when surface potential is
changing maximally; 2) the increase in peak current when Ca ions
are replaced by Sr or Ba ions; and 3) the greater inhibitory effect
of Mg on IBa than ICa. Theory indicates that surface charge cannot
be screened completely even at 1 M Mgo and thus that Ca channel
properties must be evaluated in the light of surface charge effects.
For example, after correction for surface charge effects the relative
permeabilities of Ca, Ba and Sr ions are equivalent. In the presence
of Co ions, however, Ca ions are more permeable than Ba ions suggesting
a channel binding site may be involved.
@article{Wils_1983_117,
abstract = {Calcium ions affect the gating of Ca currents. Surface charge is involved
but to what extent is unknown. We have examined this, using isolated
nerve cell bodies of Helix aspersa and the combined microelectrode-suction
pipette method for voltage-clamp and internal perfusion. We found
that Ba and Sr currents produced by substitution of these ions for
extracellular Ca ions are activated at less positive potentials than
Ca currents. Mg ions do not permeate the Ca channel and changes in
[Mg]o produce shifts in the activation-potential curves that are
comparable to the effects of changes in [Ba]o or [Sr]o. Inactivation
of Ba currents also occurs at less positive potentials. Perfusion
intracellularly with EGTA reduced inactivation of Ca currents as
a function of potential, but did not shift the inactivation-potential
curve. Hence, Ca current-dependent inactivation which is blocked
by intracellular EGTA probably does not involve a similar change
of intracellular surface potential. The voltage shifts of activation
and inactivation produced by extracellular divalent cations used
singly or in mixtures can be described by the Gouy-Chapman theory
for the diffuse double layer with binding (Gilbert & Ehrenstein,
1969; McLaughlin, Szabo & Eisenman, 1971). From the surface potential
values and the Boltzman distribution, we have computed surface concentrations
that predict the following experimental observations: 1) saturation
of current-concentration relationships when surface potential is
changing maximally; 2) the increase in peak current when Ca ions
are replaced by Sr or Ba ions; and 3) the greater inhibitory effect
of Mg on {IB}a than ICa. Theory indicates that surface charge cannot
be screened completely even at 1 M [Mg]o and thus that Ca channel
properties must be evaluated in the light of surface charge effects.
For example, after correction for surface charge effects the relative
permeabilities of Ca, Ba and Sr ions are equivalent. In the presence
of Co ions, however, Ca ions are more permeable than Ba ions suggesting
a channel binding site may be involved.},
added-at = {2009-06-03T11:20:58.000+0200},
author = {Wilson, D. L. and Morimoto, K. and Tsuda, Y. and Brown, A. M.},
biburl = {https://www.bibsonomy.org/bibtex/269c2186c5d9d53adac06ee0cbf879043/hake},
description = {The whole bibliography file I use.},
file = {Wils_1983_117.pdf:Wils_1983_117.pdf:PDF},
interhash = {db0afad96e7f3829189793b3b7098efd},
intrahash = {69c2186c5d9d53adac06ee0cbf879043},
journal = {J. Membr. Biol.},
keywords = {(Snails), 6304316 Active, Animals, Biological Biotransformation, Calcium, Channels, Gov't, Helix In Ion Magnesium, Membrane Neurons, P.H.S., Potentials, Properties, Research Support, Surface Transport, U.S. Vitro,},
number = {1-2},
pages = {117--130},
pdf = {Wils_1983_117.pdf},
pmid = {6304316},
timestamp = {2009-06-03T11:21:37.000+0200},
title = {Interaction between calcium ions and surface charge as it relates
to calcium currents.},
volume = 72,
year = 1983
}