NDLI: Glutamine Substitution at Alanine1649 in the S4–S5 Cytoplasmic Loop of Domain 4 Removes the Voltage Sensitivity of Fast Inactivation in the Human Heart Sodium Channel

Content Provider	PubMed Central
Author	Tang, Lihui Chehab, Nabil Wieland, Steven J. Kallen, Roland G.
Copyright Year	1998
Abstract	Normal activation–inactivation coupling in sodium channels insures that inactivation is slow at small but rapid at large depolarizations. M1651Q/M1652Q substitutions in the cytoplasmic loop connecting the fourth and fifth transmembrane segments of Domain 4 (S4–S5/D4) of the human heart sodium channel subtype 1 (hH1) affect the kinetics and voltage dependence of inactivation (Tang, L., R.G. Kallen, and R. Horn. 1996. J. Gen. Physiol. 108:89–104.). We now show that glutamine substitutions NH2-terminal to the methionines (L1646, L1647, F1648, A1649, L1650) also influence the kinetics and voltage dependence of inactivation compared with the wild-type channel. In contrast, mutations at the COOH-terminal end of the S4–S5/D4 segment (L1654, P1655, A1656) are without significant effect. Strikingly, the A1649Q mutation renders the current decay time constants virtually voltage independent and decreases the voltage dependences of steady state inactivation and the time constants for the recovery from inactivation. Single-channel measurements show that at negative voltages latency times to first opening are shorter and less voltage dependent in A1649Q than in wild-type channels; peak open probabilities are significantly smaller and the mean open times are shorter. This indicates that the rate constants for inactivation and, probably, activation are increased at negative voltages by the A1649Q mutation reminiscent of Y1494Q/ Y1495Q mutations in the cytoplasmic loop between the third and fourth domains (O'Leary, M.E., L.Q. Chen, R.G. Kallen, and R. Horn. 1995. J. Gen. Physiol. 106:641–658.). Other substitutions, A1649S and A1649V, decrease but fail to eliminate the voltage dependence of time constants for inactivation, suggesting that the decreased hydrophobicity of glutamine at either residues A1649 or Y1494Y1495 may disrupt a linkage between S4–S5/D4 and the interdomain 3–4 loop interfering with normal activation–inactivation coupling.
Starting Page	639
File Format	PDF
ISSN	15407748
e-ISSN	15407748
Journal	The Journal of General Physiology
Issue Number	5
Volume Number	111
Language	English
Publisher	The Rockefeller University Press
Publisher Date	1998-05-01
Access Restriction	Open
Rights Holder	The Rockefeller University Press
Subject Keyword	Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physiology

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