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. 1995 Jan;68(1):111–120. doi: 10.1016/S0006-3495(95)80165-7

Measuring the length of the pore of the sheep cardiac sarcoplasmic reticulum calcium-release channel using related trimethylammonium ions as molecular calipers.

A Tinker 1, A J Williams 1
PMCID: PMC1281667  PMID: 7536054

Abstract

After incorporation of purified sheep cardiac Ca(2+)-release channels into planar phospholipid bilayers, we have investigated the blocking effects of a series of monovalent (CH3-(CH2)n-1-N+(CH3)3) and divalent ((CH3)3N(+)-(CH2)n-N+(CH3)3) trimethylammonium derivatives under voltage clamp conditions. All the compounds tested produce voltage-dependent block from the cytoplasmic face of the channel. With divalent (Qn) derivatives the effective valence of block decreases with increasing chain length, reaching a plateau with a chain length of n > or = 7. No decline in effective valence is observed with the monovalent (Un) derivatives. A plausible interpretation of this phenomena suggests that for the 90% of the voltage drop measured, the increase in length following the addition of a CH2 in the chain spans 12.7% of the electrical field. Extrapolating this distance to include the remaining 10% suggests that the applied holding potential falls over a total distance of 10.4 A. In addition, at high positive holding potentials there is evidence for permeation of the trimethylammonium ions and a valency specific relief of block.

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114FIGURE 2
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115FIGURE 5
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Selected References

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