In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 98, No. 12 ( 2001-06-05), p. 6935-6940
Abstract:
To investigate the molecular basis of the voltage sensor that
triggers excitation–contraction (EC) coupling, the four-domain pore subunit of the dihydropyridine receptor (DHPR) was cut in the
cytoplasmic linker between domains II and III. cDNAs for the I-II domain (α1S 1–670) and the III-IV domain (α1S 701-1873) were
expressed in dysgenic α1S-null myotubes. Coexpression of the two fragments resulted in complete recovery of DHPR intramembrane charge
movement and voltage-evoked Ca 2+ transients. When fragments
were expressed separately, EC coupling was not recovered. However, charge movement was detected in the I-II domain expressed alone.
Compared with I-II and III-IV together, the charge movement in the I-II
domain accounted for about half of the total charge ( Q max = 3 ± 0.23 vs. 5.4 ±
0.76 fC/pF, respectively), and the half-activation potential for charge movement was significantly more negative
( V 1/2 = 0.2 ± 3.5 vs. 22 ±
3.4 mV, respectively). Thus, interactions between the four internal domains of the pore subunit in the assembled DHPR profoundly affect the
voltage dependence of intramembrane charge movement. We also tested a two-domain I-II construct of the neuronal α1A Ca 2+ channel. The neuronal I-II domain recovered charge movements like those
of the skeletal I-II domain but could not assist the skeletal III-IV domain in the recovery of EC coupling. The results demonstrate that a
functional voltage sensor capable of triggering EC coupling in skeletal myotubes can be recovered by the expression of complementary fragments
of the DHPR pore subunit. Furthermore, the intrinsic voltage-sensing properties of the α1A I-II domain suggest that this
hemi-Ca 2+ channel could be relevant to neuronal function.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.111001898
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2001
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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