TY - JOUR
T1 - Evidence for a direct interaction between internal tetra-alkylammonium cations and the inactivation gate of cardiac sodium channels
AU - O’Leary, Michael E.
AU - Kallen, Roland G.
AU - Horn, Richard
N1 - Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 1994/9/1
Y1 - 1994/9/1
N2 - The effects of internal tetrabutylammonium (TBA) and tetrapentylammonium (TPeA) were studied on human cardiac sodium channels (hill) expressed in a mammalian tsA201 cell line. Outward currents were measured at positive voltages using a reversed Na gradient. TBA and TPeA cause a concentration-dependent increase in the apparent rate of macroscopic Na current inactivation in response to step depolarizations. At TPeA concentrations < 50 µM the current decay is well fit by a single exponential over a wide voltage range. At higher concentrations a second exponential component is observed, with the fast component being dominant. The blocking and unblocking rate constants of TPeA were estimated from these data, using a three-state kinetic model, and were found to be voltage dependent. The apparent inhibition constant at 0 mV is 9.8 µM, and the blocking site is located 41 ±3% of the way into the membrane field from the cytoplasmic side of the channel. Raising the external Na concentration from 10 to 100 mM reduces the TPeA-modified inactivation rates, consistent with a mechanism in which external Na ions displace TPeA from its binding site within the pore. TBA (500 µM) and TPeA (20 µM) induce a use-dependent block of Na channels characterized by a progressive, reversible, decrease in current amplitude in response to trains of depolarizing pulses delivered at 1-s intervals. Tetrapropylammonium (TPrA), a related symmetrical tetra-alkylammonium (TAA), blocks Na currents but does not alter inactivation (O’Leary, M. E., and R. Horn. 1994. Journal of General Physiology. 104:507-522.) or show use dependence. Internal TPrA antagonizes both the TPeA-induced increase in the apparent inactivation rate and the use dependence, suggesting that all TAA compounds share a common binding site in the pore. A channel blocked by TBA or TPeA inactivates at nearly the normal rate, but recovers slowly from inactivation, suggesting that TBA or TPeA in the blocking site can interact directly with a cytoplasmic inactivation gate.
AB - The effects of internal tetrabutylammonium (TBA) and tetrapentylammonium (TPeA) were studied on human cardiac sodium channels (hill) expressed in a mammalian tsA201 cell line. Outward currents were measured at positive voltages using a reversed Na gradient. TBA and TPeA cause a concentration-dependent increase in the apparent rate of macroscopic Na current inactivation in response to step depolarizations. At TPeA concentrations < 50 µM the current decay is well fit by a single exponential over a wide voltage range. At higher concentrations a second exponential component is observed, with the fast component being dominant. The blocking and unblocking rate constants of TPeA were estimated from these data, using a three-state kinetic model, and were found to be voltage dependent. The apparent inhibition constant at 0 mV is 9.8 µM, and the blocking site is located 41 ±3% of the way into the membrane field from the cytoplasmic side of the channel. Raising the external Na concentration from 10 to 100 mM reduces the TPeA-modified inactivation rates, consistent with a mechanism in which external Na ions displace TPeA from its binding site within the pore. TBA (500 µM) and TPeA (20 µM) induce a use-dependent block of Na channels characterized by a progressive, reversible, decrease in current amplitude in response to trains of depolarizing pulses delivered at 1-s intervals. Tetrapropylammonium (TPrA), a related symmetrical tetra-alkylammonium (TAA), blocks Na currents but does not alter inactivation (O’Leary, M. E., and R. Horn. 1994. Journal of General Physiology. 104:507-522.) or show use dependence. Internal TPrA antagonizes both the TPeA-induced increase in the apparent inactivation rate and the use dependence, suggesting that all TAA compounds share a common binding site in the pore. A channel blocked by TBA or TPeA inactivates at nearly the normal rate, but recovers slowly from inactivation, suggesting that TBA or TPeA in the blocking site can interact directly with a cytoplasmic inactivation gate.
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U2 - 10.1085/jgp.104.3.523
DO - 10.1085/jgp.104.3.523
M3 - Article
C2 - 7807060
AN - SCOPUS:0028024516
VL - 104
SP - 523
EP - 539
JO - Journal of General Physiology
JF - Journal of General Physiology
SN - 0022-1295
IS - 3
ER -