Inactivation of L-type calcium channels is determined by the length of the N terminus of mutant beta(1) subunits.
Voltage-dependent calcium channel (Ca(v)) pores are modulated by cytosolic beta subunits. Four beta-subunit genes and their splice variants offer a wide structural array for tissue- or disease-specific biophysical gating phenotypes. For instance, the length of the N terminus of beta(2) subunits has major effects on activation and inactivation rates. We tested whether a similar mechanism principally operates in a beta(1) subunit. Wild-type beta(1a) subunit (N terminus length 60 aa) and its newly generated N-terminal deletion mutants (51, 27 and 18 aa) were examined within recombinant L-type calcium channel complexes (Ca(v)1.2 and alpha(2)delta2) in HEK293 cells at the whole-cell and single-channel level. Whole-cell currents were enhanced by co-transfection of the full-length beta(1a) subunit and by all truncated constructs. Voltage dependence of steady-state activation and inactivation did not depend on N terminus length, but inactivation rate was diminished by N terminus truncation. This was confirmed at the single-channel level, using ensemble average currents. Additionally, gating properties were estimated by Markov modeling. In confirmation of the descriptive analysis, inactivation rate, but none of the other transition rates, was reduced by shortening of the beta(1a) subunit N terminus. Our study shows that the length-dependent mechanism of modulating inactivation kinetics of beta(2) calcium channel subunits can be confirmed and extended to the beta(1) calcium channel subunit.
Jangsangthong
Wanchana
W
Department of Pharmacology, University of Cologne, Gleueler Strasse 24, 50931 Cologne, Germany.
Kuzmenkina
Elza
E
Khan
Ismail F Y
IF
Matthes
Jan
J
Hullin
Roger
R
Herzig
Stefan
S
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008390:Markov Chains; D008969:Molecular Sequence Data; D009154:Mutation; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism
D020746:Calcium Channels, L-Type; D020033:Protein Isoforms; D021122:Protein Subunits