Modulation of Ionic Selectivity of Ca Channels in the Neuronal Membrane by Ca Ions

Mironov, S.L.

doi:10.1007/978-1-4613-0975-8_4

Cited by 2 publications

(4 citation statements)

References 12 publications

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“…14 and this paper) can also be explained in terms of this hypothesis (3). One qualitative prediction ofthis model is that Ca channel currents carried by mixtures of Ca and Ba should display extra noise as the instantaneous current switches back and forth between i(3 mM Ca) and i(7 mM Ba).…”

Section: Methodsmentioning

confidence: 62%

“…Comparison with a Model Pore with Only One Intrapore Binding Site. Kostyuk and Mironov (10) and Mironov (3) have proposed an explanation for the AMFE in terms of a model pore with only one intrapore binding site for permeant ions (see also ref. 11).…”

Section: Methodsmentioning

confidence: 99%

“…refs. [6][7][8]; other models invoke allosteric interactions between a single intrapore binding site and an external regulatory ion binding site (3,(9)(10)(11). All of these models are constrained in an important way by experimental findings of an AMFE.…”

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confidence: 99%

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Voltage-gated calcium channels: direct observation of the anomalous mole fraction effect at the single-channel level.

Friel

Tsien

1989

Proc. Natl. Acad. Sci. U.S.A.

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The AMFE has been observed in whole-cell recordings of high-voltage-activated Ca current from cardiac myocytes, skeletal muscle, and neurons (4, 5, 12, 13). However, there has been little direct evidence for anomalous mole fraction behavior at the level of single channels, apart from ChesnoyMarchais' study (14) of a Ca-permeable channel active at even very negative membrane potentials in Aplysia neurons. In L-type Ca channels, the main focus of work on Ca channel permeation, experimental support for the AMFE has been restricted to fluctuation analysis (4). Recently, Yue and Marban (15, 16) looked at unitary currents through cardiac L-type Ca channels. Unable to find the AMFE at the singlechannel level, they suggested that the previous whole-cell evidence for the AMFE data might reflect ion-dependent changes in gating and that models of Ca channel permeation may need radical revision.We have looked for an AMFE in recordings from L-type Ca channels in PC-12 pheochromocytoma cells. Our results demonstrate a significant AMFE at the single-channel level, but only under restrictive conditions of permeant ion concentration (Ct) and membrane potential (V). METHODSRecording Conditions. L-type Ca channel currents were recorded from PC-12 cells grown without nerve growth factor as described (17) except that Dulbecco's modified Eagle's medium (GIBCO) replaced RPMI 1640. Cells were grown at low density on glass coverslips coated with rat-tail collagen (Biomedical Technologies, Stoughton, MA) and poly(Dlysine) (GIBCO). Whole-cell and single-channel currents were measured by the patch-clamp technique (18) with solutions as described in the figure legends. Ca agonists were included to promote L-type channel activity and long, easily resolved channel openings.Current Measurements. All currents were measured with a List EPC-7 voltage clamp. Whole-cell currents were filtered at 1.0 kHz (8-pole Bessel, -3 decibel), digitized at 5 kHz, and stored on a laboratory computer. Currents were elicited from -40 mV to promote inactivation of Ca channels other than L-type (19-21) and were measured at potentials ranging from -40 to +20 mV by either (i) depolarizing from a negative holding potential, (ii) repolarizing from a depolarized potential, or (iii) depolarizing steadily. Currents were filtered at 0.3, 0.5, or 1.0 kHz and digitized at 2 or 5 kHz. Recordings were done at room temperature (-22°C

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Section: Methodsmentioning

confidence: 62%

Section: Methodsmentioning

confidence: 99%

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Voltage-gated calcium channels: direct observation of the anomalous mole fraction effect at the single-channel level.

Friel

Tsien

1989

Proc. Natl. Acad. Sci. U.S.A.

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“…For a channel with a unique saturable binding site, single-channel currents for mixtures of permeant ions could be described as the weighted sum (according to the mole fraction) of the current due to each individual ion: if ions A and B, at a total concentration of Ct, are characterized by single-channel currents ia and in, then the current in a solution of allosteric effects (22,63,64,88), the most commonly accepted explanation that the permeant ions are interacting within the lumen of a single-file pore. The anomalous mole-fraction effect exists, like the frank blockade described in the next section, when one ionic species occupies the channel and prevents another from permeating it.…”

Section: Anomalous Mole-fraction Effectsmentioning

confidence: 99%

Strategies For Studying Permeation At Voltage-Gated Ion Channels

Lester¹

1991

Annual Review of Physiology

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Modulation of Ionic Selectivity of Ca Channels in the Neuronal Membrane by Ca Ions

Cited by 2 publications

References 12 publications

Voltage-gated calcium channels: direct observation of the anomalous mole fraction effect at the single-channel level.

Voltage-gated calcium channels: direct observation of the anomalous mole fraction effect at the single-channel level.

Strategies For Studying Permeation At Voltage-Gated Ion Channels

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