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TRPC5 channels undergo changes in gating properties during the activation‐deactivation cycle
Author(s) -
Obukhov Alexander G.,
Nowycky Martha C.
Publication year - 2008
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.21388
Subject(s) - gating , trpc5 , chemistry , biophysics , phase (matter) , conductance , ion channel , trpc1 , physics , biochemistry , receptor , biology , organic chemistry , condensed matter physics
TRPC5 are non‐specific cation channels activated through phospholipase C‐dependent pathways, although the precise gating mechanism is unknown. TRPC5 current–voltage relationships (I–Vs) change systematically during the activation‐deactivation cycle, shifting between outwardly rectifying and doubly rectifying shapes. Since several TRP family members exhibit voltage‐dependent properties, we investigated whether the various I–V relationships were due to changes in gating. Using patch‐clamp recordings of rat TRPC5 transfected HEK293 cells, we found that TRPC5 currents had distinct biophysical characteristics correlated with individual I–V shapes, a phenomenon we call ‘phases.’ At rest, channels were closed at most potentials, although strong depolarizations (>+80 mV) stimulated small outward currents (Phase 0). For 10–15 sec after activation, voltage steps evoked small inward and large outward currents with time‐ and voltage‐dependent kinetics (Phase 1, outwardly‐rectifying I–Vs). At maximal inward amplitude, currents were voltage‐independent at all potentials (Phase 2, doubly‐rectifying I–Vs owing to Mg 2+ block). During desensitization (Phase 3), currents reverted to a Phase 1‐like voltage‐dependence. La 3+ ions potentiated inward TRPC5 currents by promoting a reversible transition from Phase 3 to Phase 2. Single channel recordings revealed asymmetric conductance properties with values of ∼40 pS at negative potentials and ∼130 pS at >+60 mV. Mutation of D633, a cytoplasmic residue that mediates Mg 2+ block, decreased channel activity at negative potentials during Phase 2. We conclude that TRPC5 gating properties can switch reversibly between voltage‐dependent and voltage‐independent states. The modulation of phase transitions by external agents such as La 3+ and EBP50, a scaffolding protein, may constitute a novel mechanism for regulation of channel activity. J. Cell. Physiol. 216: 162–171, 2008. © 2008 Wiley‐Liss, Inc.