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The presence of ca 2+ channel β subunit is required for mitogen‐activated protein kinase (mapk)‐dependent modulation of α1b ca 2+ channels in cos‐7 cells
Author(s) -
Fitzgerald Elizabeth M.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.022822
Subject(s) - mapk/erk pathway , protein kinase a , protein subunit , biophysics , kinase , voltage dependent calcium channel , chemistry , microbiology and biotechnology , biology , calcium , biochemistry , organic chemistry , gene
In rat sensory neurones, voltage‐dependent calcium channels (VDCCs), including the N‐type, are tonically up‐regulated via Ras/mitogen‐activated protein kinase (MAPK) signalling. To determine whether VDCC β subunit is involved in this process, the role of the four neuronal βs (β1b, β2a, β3, β4) in MAPK‐dependent modulation of α1B (Ca v 2.2, N‐type) Ca 2+ channels has been examined in COS‐7 cells. MAPK is exclusively activated by MAPK kinase (MEK), and here, acute application of a MEK‐specific inhibitor UO126, significantly inhibited peak α1B Ca 2+ channel current ( I max ) within a period of 5–10 min, regardless of which β subunit was co‐expressed (25‐50%, P < 0.01). With β2a however, the percentage inhibition of I max was less than that observed with any other β (ANOVA: F 3,34 = 6.48, P < 0.01). UO126 also caused a hyperpolarising shift (6 ± 1 mV, P < 0.001) in the voltage dependence of β2a current activation, such that inhibition occurred only at depolarised potentials (> +5 mV) whereas at more negative potentials the current amplitude was enhanced. A marked change in β2a current kinetics, perceived either as decreased activation or increased inactivation, was also associated with UO126 application. A similar effect of UO126 on β4 current kinetics was also observed. The β2a‐specific effects of UO126 on current inhibition and voltage dependence of activation were abolished when α1B was co‐expressed with de‐palmitoylated β2a(C3,4S), in which amino terminal cysteines 3 and 4 had been mutated to serines. In the absence of β subunit, UO126 had no effect on α1B Ca 2+ channel current. Together, these data suggest an absolute requirement for β in MAPK‐dependent modulation of these channels. Since β subunits vary both in their temporal expression and localisation within neurones, β subunit‐dependent modulation of N‐type Ca 2+ channels via MAPK could provide an important new mechanism by which to fine‐tune neurotransmitter release.