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1. The ion selectivity of a membrane ion conductance that is inactivated by extracellular calcium (Ca2+o) in Xenopus oocytes has been studied using the voltage-clamp technique. 2. The reversal potential of the Ca2+o-sensitive current (Ic) was measured using voltage ramps (-80 to +40 mV) as a function of the external concentration (12-240 mM) of NaCl or KCl. The direction and amplitude of the shifts in reversal potentials are consistent with permeability ratios of 1:0.99:0.24 for K+:Na+:Cl-. 3. Current-voltage (I-V ) relations of Ic, determined during either voltage ramps of 0.5 s duration or at steady state, displayed pronounced rectification at both hyperpolarized and depolarized potentials. However, instantaneous I-V relations showed less rectification and could be fitted by the constant field equation assuming the above K+:Na+:Cl- permeability ratios. 4. Ion substitution experiments indicated that relatively large organic monovalent cations and anions are permeant through Ic channels with the permeability ratios K+:NMDG+:TEA+:TPA+:TBA+:Gluc- = 1:0.45:0. 35:0.2:0.2:0.2. 5. External amiloride (200 microM), gentamicin (220 microM), flufenamic acid (40 microM), niflumic acid (100 microM), Gd3+ (0.3 microM) or Ca2+ (200 microM) caused reversible block of Ic without changing its reversal potential. 6. Preinjection of oocytes with antisense oligonucleotide against connexin 38, the Xenopus hemi-gap-junctional protein, inhibited Ic by 80 % without affecting its ion selectivity, thus confirming and extending the recent suggestion of Ebihara that Ic represents current carried through hemi-gap-junctional channels. 7. In vitro and in vivo maturation of oocytes resulted in a significant decrease in Ic conductance to 7 % and 2 % of control values, respectively. This developmental downregulation of Ic minimizes any toxic effect Ic activation would have when the mature egg is released into Ca2+o-free pond water. 8. The results of this study are discussed in relation to other Ca2+o-inactivated conductances seen in a wide variety of cell types and which have previously been interpreted as arising either from Ca2+o-masked channels or from changes in the ion selectivity of voltage-gated Ca2+ or K+ channels.
Almers,
A non-selective cation conductance in frog muscle membrane blocked by micromolar external calcium ions.
1984, Pubmed
Almers,
A non-selective cation conductance in frog muscle membrane blocked by micromolar external calcium ions.
1984,
Pubmed
Arellano,
Functional role of follicular cells in the generation of osmolarity-dependent Cl- currents in Xenopus follicles.
1995,
Pubmed
,
Xenbase
Arellano,
A monovalent cationic conductance that is blocked by extracellular divalent cations in Xenopus oocytes.
1995,
Pubmed
,
Xenbase
Armstrong,
Do voltage-dependent K+ channels require Ca2+? A critical test employing a heterologous expression system.
1990,
Pubmed
Beblo,
Monovalent cation permeation through the connexin40 gap junction channel. Cs, Rb, K, Na, Li, TEA, TMA, TBA, and effects of anions Br, Cl, F, acetate, aspartate, glutamate, and NO3.
1997,
Pubmed
Borisova,
Mechanism of anion-cation selectivity of amphotericin B channels.
1986,
Pubmed
Bruzzone,
Connections with connexins: the molecular basis of direct intercellular signaling.
1996,
Pubmed
Dascal,
The use of Xenopus oocytes for the study of ion channels.
1987,
Pubmed
,
Xenbase
DeVries,
Hemi-gap-junction channels in solitary horizontal cells of the catfish retina.
1992,
Pubmed
Ebihara,
Xenopus connexin38 forms hemi-gap-junctional channels in the nonjunctional plasma membrane of Xenopus oocytes.
1996,
Pubmed
,
Xenbase
Ebihara,
Cloning and expression of a Xenopus embryonic gap junction protein.
1989,
Pubmed
,
Xenbase
Ebihara,
Distinct behavior of connexin56 and connexin46 gap junctional channels can be predicted from the behavior of their hemi-gap-junctional channels.
1995,
Pubmed
,
Xenbase
Franciolini,
A multi-ion permeation mechanism in neuronal background chloride channels.
1994,
Pubmed
Grissmer,
Divalent ion trapping inside potassium channels of human T lymphocytes.
1989,
Pubmed
Guo,
A sustained inward current activated at the diastolic potential range in rabbit sino-atrial node cells.
1995,
Pubmed
Halm,
Anion permeation in an apical membrane chloride channel of a secretory epithelial cell.
1992,
Pubmed
Hamill,
Rapid adaptation of single mechanosensitive channels in Xenopus oocytes.
1992,
Pubmed
,
Xenbase
Hamill,
The pharmacology of mechanogated membrane ion channels.
1996,
Pubmed
Ishihara,
Toad egg-jelly as a source of divalent cations essential for fertilization.
1984,
Pubmed
Krenacs,
Direct cell/cell communication in the lymphoid germinal center: connexin43 gap junctions functionally couple follicular dendritic cells to each other and to B lymphocytes.
1997,
Pubmed
Li,
Properties and regulation of gap junctional hemichannels in the plasma membranes of cultured cells.
1996,
Pubmed
Lindsay,
Proteases released from Xenopus laevis eggs at activation and their role in envelope conversion.
1989,
Pubmed
,
Xenbase
McLaughlin,
The electrostatic properties of membranes.
1989,
Pubmed
Mubagwa,
Extracellular divalent cations block a cation non-selective conductance unrelated to calcium channels in rat cardiac muscle.
1997,
Pubmed
Pappone,
Alpha-adrenergic stimulation activates a calcium-sensitive chloride current in brown fat cells.
1995,
Pubmed
Reifarth,
The Ca2+-inactivated Cl- channel at work: selectivity, blocker kinetics and transport visualization.
1997,
Pubmed
,
Xenbase
Sandberg,
Intercellular communication between follicular angiotensin receptors and Xenopus laevis oocytes: medication by an inositol 1,4,5-trisphosphate-dependent mechanism.
1992,
Pubmed
,
Xenbase
Stühmer,
Electrophysiological recording from Xenopus oocytes.
1992,
Pubmed
,
Xenbase
Trexler,
Voltage gating and permeation in a gap junction hemichannel.
1996,
Pubmed
,
Xenbase
Tupper,
The ionic permeability of the amphibian oocyte in the presence or absence of external calcium.
1973,
Pubmed
Van Driessche,
Cation-selective channels in amphibian epithelia: electrophysiological properties and activation.
1988,
Pubmed
Veenstra,
Selectivity of connexin-specific gap junctions does not correlate with channel conductance.
1995,
Pubmed
Wang,
Monovalent ion selectivity sequences of the rat connexin43 gap junction channel.
1997,
Pubmed
Weber,
The Ca(2+)-induced leak current in Xenopus oocytes is indeed mediated through a Cl- channel.
1995,
Pubmed
,
Xenbase
Weber,
Influence of extracellular Ca2+ on endogenous Cl- channels in Xenopus oocytes.
1995,
Pubmed
,
Xenbase
Zambrowicz,
Zero-current potentials in a large membrane channel: a simple theory accounts for complex behavior.
1993,
Pubmed
Zhang,
The ion selectivity of a membrane conductance inactivated by extracellular calcium in Xenopus oocytes.
1998,
Pubmed
,
Xenbase
Zhou,
Identification of a pore lining segment in gap junction hemichannels.
1997,
Pubmed
,
Xenbase
