Block of neuronal fast chloride channels by internal tetraethylammonium ions.

Abstract

A B S T R A C T The classical potassium-selective ion channel blocker tetraethylammonium ion (TEA) was shown to block chloride-selective ion channels from excised surface membranes of acutely dissociated rat cortical neurons when applied to the formerly intracellular membrane surface. The patch voltage clamp method was used to record single channel currents from fast C1 channels in the presence of TEAi. 'At the filtering cut-off frequencies used (3-12.4 kHz, -3 dB) the TEAi-induced block appeared as a reduction in single channel current amplitude, which was interpreted as the result of extremely fast on and off rates for the blocking reaction. Under the conditions of these experiments, the magnitude of TEAi block was independent of membrane potential. Analysis of dose-response experimental results suggests that TEA binding resulted in a partial block of these channels with an equilibrium dissociation constant of ~ 12-15 mM. Analysis of amplitude distributions in the absence and presence of TEA~ using the method of Yellen (1994. Journal of General Physiology. 84:157-186.) produced a similar equilibrium dissociation constant and provided a blocking rate constant of ~ 16,000 mM-I's -1 and an unblocking rate constant of ~200,000 s -*. The distributions of open and closed interval durations were fit with a blocking scheme where TEAi binds to the open kinetic state with the constraint that the channel must reenter the open state before TEA can dissociate. The increase in the mean lifetime of the open state could be well fit by this model, but the distribution of closed interval durations could not, suggesting a more complex underlying blocking mechanism.

Role for calcium‐activated potassium channels (BK) in growth control of human malignant glioma cells

“…This correlates well with previous electrophysiology data showing an IC 50 of about 8 nM for IbTX (Ransom and Sontheimer, 2001). Although both TEA and IbTX were able to elicit this effect, we performed the remainder of our analysis solely in the presence of IbTX because it has been shown to be a selective inhibitor of large‐conductance, calcium‐activated, voltage‐dependent (BK) potassium channels (Galvez et al, 1990), whereas TEA has the potential to block other K + (Hille, 2001) and Cl − channels (Sanchez and Blatz, 1992, 1994) as well.…”

Bupivacaine inhibits large conductance, voltage- and Ca2+- activated K+channels in human umbilical artery smooth muscle cells

“…The K D calculated for different membrane potentials were statistically different and Figure 1F shows these values plotted as a function of the membrane potential. This relationship was well-fitted by an exponential decay function: 12,13 where K D (0) is the K D value at 0 mV, z is the valence of the blocker (+1 in this case), V is the voltage across the membrane, δ is the location of the blocking site in terms of the fraction of the electrical field (the electrical distance) measured from the inside of the membrane, and RT/f = 25.3 mV at 22°C. A K D (0) of 1,444 μM and a δ of 0.46 were obtained from the best fit to the graph shown in Figure 1F.…”

“…12,13 From this equation, one can obtain the drug dissociation constant (K D ) which represents the bupivacaine concentration that produces 50% current inhibition (IC 50 ) at each membrane potential. The K D calculated for different membrane potentials were statistically different and Figure 1F shows these values plotted as a function of the membrane potential.…”

Chlorotoxin does not inhibit volume‐regulated, calcium‐activated and cyclic AMP‐activated chloride channels

“…Sanchez & Blatz (1992; 1994) demonstrated that external and internal TEA inhibits neuronal fast Cl − channels. The biophysical and pharmacological profile of this channel is however completely different from that of GCC.…”