Altered expression and assembly of N-type calcium channel alpha1B and beta subunits in epileptic lethargic (lh/lh) mouse.
Voltage-dependent calcium channels (VDCC) are multisubunit complexes whose expression and targeting require the assembly of the pore-forming alpha1 with auxiliary beta and alpha2/delta subunits. The developmentally regulated expression and differential assembly of beta isoforms with the alpha1B subunit to form N-type VDCC suggested a unique role for the beta4 isoform in VDCC maturation (Vance, C. L., Begg, C. M., Lee, W.-L., Haase, H., Copeland, T. D., and McEnery, M. W. (1998) J. Biol. Chem. 273, 14495-14502). The focus of this study is the expression and assembly of alpha1B and beta isoforms in the epileptic mouse, lethargic (lh/lh), a mutant anticipated to produce a truncated beta4 subunit (Burgess, D. L., Jones, J. M., Meisler, M. H., and Noebels, J. L. (1997) Cell 88, 385-392). In this report, we demonstrate that neither full-length nor truncated beta4 protein is expressed in lh/lh mice. The absence of beta4 in lh/lh mice is associated with decreased expression of N-type VDCC in forebrain and cerebellum. The most surprising characteristic of the lh/lh mouse is increased expression of beta1b protein. This result suggests a previously unidentified cellular mechanism wherein expression of the total pool of available beta subunits is under tight metabolic regulation. As a consequence of increased beta1b expression, the beta1b is increased in its incorporation into alpha1B/beta complexes relative to wild type. Thus, in striking similarity to the population of N-type VDCC present in immature rat brain, the population of N-type VDCC present in adult lh/lh mice is characterized by the absence of beta4 with increased beta1b expression and assembly into N-type VDCC. It is intriguing to speculate that the increased excitability and susceptibility to seizures observed in the lh/lh mouse arises from the inappropriate expression of an immature population of N-type VDCC throughout neuronal development.
McEnery
M W
MW
Department of Physiology and Biophysics, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106-4970, USA. mwm4@po.cwru.edu
Copeland
T D
TD
Vance
C L
CL
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000096:biosynthesis* / Q000235:genetics; D004827:Epilepsy / Q000378:metabolism*; D051379:Mice; D008818:Mice, Neurologic Mutants; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D011487:Protein Conformation; D051381:Rats; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010455:Peptides; D020866:omega-Conotoxin GVIA