Stilbene disulfonate blockade of colonic secretory Cl- channels in planar lipid bilayers.
We studied blockade by 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS) of a secretory Cl- channel from colonic enterocyte plasma membrane vesicles incorporated into planar lipid bilayer membranes. Except for intermittent long-lived closed periods (100 ms to several min), the control channel open probability (Po) was greater than 90%. DNDS, added to the cis or vesicle-containing side, which corresponds to the outer membrane side of the channel, caused a dramatic increase in the number of current transitions from the open-to-closed state. DNDS caused a concentration-dependent decrease in Po with a maximum inhibition of 95 +/- 2.0% and a half-maximal inhibitory concentration of 3.3 +/- 1.4 microM. DNDS added to the trans side of the channel had no effect on either the single-channel conductance or kinetic behavior of the channel. Kinetic analysis revealed that DNDS blockade from the cis side could be explained by a linear, closed-open-blocked, kinetic scheme. The estimated DNDS block rate constants were kon = 3.2 X 10(7) M-1.s-1 and koff = 52 s-1, yielding an equilibrium dissociation constant (KD) of 2.1 +/- 0.38 microM, similar to the Ki for inhibition of Po. The effects of DNDS were fully reversible after perfusion of the cis compartment with DNDS-free solution. In contrast, the covalently reactive 4,4'-diisothiocyano-substituted stilbene disulfonate caused an irreversible blockade of the Cl- channel.[1]References
- Stilbene disulfonate blockade of colonic secretory Cl- channels in planar lipid bilayers. Bridges, R.J., Worrell, R.T., Frizzell, R.A., Benos, D.J. Am. J. Physiol. (1989) [Pubmed]
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