COMMUNICATION
Altered Expression and Assembly of N-type Calcium Channel alpha 1B and beta  Subunits in Epileptic lethargic (lh/lh) Mouse*

Maureen W. McEneryDagger §, Terry D. Copeland, and Courtney L. VanceDagger

From the Dagger  Department of Physiology and Biophysics, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106-4970 and  ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, National Institutes of Health, Frederick, Maryland 21702

    ABSTRACT
Top
Abstract
Introduction
Procedures
Results & Discussion
References

Voltage-dependent calcium channels (VDCC) are multisubunit complexes whose expression and targeting require the assembly of the pore-forming alpha 1 with auxiliary beta  and alpha 2/delta subunits. The developmentally regulated expression and differential assembly of beta  isoforms with the alpha 1B subunit to form N-type VDCC suggested a unique role for the beta 4 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 alpha 1B and beta  isoforms in the epileptic mouse, lethargic (lh/lh), a mutant anticipated to produce a truncated beta 4 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 beta 4 protein is expressed in lh/lh mice. The absence of beta 4 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 beta 1b 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 beta 1b expression, the beta 1b is increased in its incorporation into alpha 1B/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 beta 4 with increased beta 1b 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.

    INTRODUCTION
Top
Abstract
Introduction
Procedures
Results & Discussion
References

There has been continued effort to determine the molecular origin of epileptic seizures with the objective of identifying new therapeutic strategies (1). Recently, attention has been directed to epileptic strains of animals that exhibit absence seizures with electrographic firing patterns, onset, localization, and drug response similar to humans (2). Genetic analysis of the mouse strains tottering (tg) and leaner (ln) (3, 4) has identified mutations in the alpha 1A subunit, which, upon assembly with beta  and alpha 2/delta subunits (5), constitutes P/Q-type voltage-dependent calcium channels (VDCC).1 Mutations in the human alpha 1A gene, however, do not appear to be the locus of common idiopathic generalized epilepsy (6). It is important to consider that although mutations in alpha 1 have been demonstrated to alter the biophysical properties of the VDCC (7), in vitro recombinant studies have reported modification of VDCC properties that are a consequence of differential association of alpha 1 with specific beta  subunit isoforms (8).

These observations are significant in light of the recent report that mutation of the beta 4 subunit is the molecular defect in the epileptic mouse strain lethargic (lh/lh) (9). The phenotype of homozygous lh/lh mice includes absence seizures, instability of gait, and convulsions (10, 11). In contrast to the calcium channelopathies that underlie human spinocerebellar ataxia (SCA6) (12, 13) and leaner (3, 4), the cerebellum of the lh/lh mouse is structurally normal (10). Importantly, the lh gene is anticipated to produce a truncated beta 4 protein that does not possess a consensus alpha 1 binding domain that mediates alpha 1/beta interaction (14), suggesting that a defect in VDCC assembly underlies the pathogenesis of the lh/lh phenotype.

There is little information available on the mechanisms that regulate the level of expression of beta  isoforms and their assembly with alpha 1. Assembly of N-type VDCC subunits has been analyzed in several developing and differentiating systems (15). During IMR32 cell differentiation, beta 1b was up-regulated and increased in parallel with the expression of alpha 1B (16). Expression of beta isoforms is also highly regulated during rat brain ontogeny, with beta 1b increasing approximately 3-fold and beta 4 increasing 10-fold during the interval between postnatal day 2 (P2) and adult (17). Postnatal assembly of beta  isoforms with alpha 1B to form N-type VDCC indicated differential association of beta  isoforms in immature versus mature forebrain homogenates. beta 1b was the predominant beta  detected in assembled immature N-type VDCC at P2 (17). beta 4 was not detected as a component of immature N-type VDCC and was incorporated into mature N-type VDCC with a time course that paralleled its expression (17). Thus, differences in the beta  component of the N-type VDCC defined both an immature and a mature population of N-type VDCC (17). Although the significance of beta  heterogeneity has not been fully explored in vivo, these developmental studies suggested a unique role of beta 4 in N-type VDCC maturation. The lh/lh mouse offers the opportunity to study patterns of beta  isoform expression that occur in response to abnormal expression of beta 4. The focus of this study is the level of alpha 1B and beta  subunit expression and assembly of N-type VDCC in the lh/lh mouse with emphasis upon identifying possible compensatory mechanisms that occur from altered beta 4 expression.

    EXPERIMENTAL PROCEDURES
Top
Abstract
Introduction
Procedures
Results & Discussion
References

Lethargic (B6EiC3H-a/A-lh) and wild-type mice (strain B6EiC3H) were obtained from Jackson Labs. All reagents were obtained from sources previously cited (17). Adult mice were euthanized in accordance with accepted university guidelines, and the brains were removed and immediately placed in 50 mM Hepes, pH 7.4, 1 mM EGTA plus protease inhibitor mixture (17). The tissues were homogenized with a Polytron homogenizer for 10 s and centrifuged at 18,000 rpm (48,000 × g) for 15 min. The membranes were resuspended in 50 mM Hepes, pH 7.4, plus protease inhibitors at a resulting protein concentration of 50 mg/ml. The N-type VDCC was solubilized from forebrain and cerebellar membranes of wild-type and lh/lh mice as described previously (18). For Western blot analysis, all homogenates were stored at -20 °C at concentrations of 2 mg/ml in sample buffer (5× sample buffer: 325 mM Tris, pH 7.0, glycerol (25% v/v), mercaptoethanol (25% v/v), SDS (10%)) in 100-µl aliquots. The samples were not freeze-thawed. The production of anti-peptide polyclonal antibodies to VDCC subunit epitopes has been described previously (16, 17, 19, 20). Methods for 125I-CTX binding, Scatchard analysis (21, 22), quantitative Western blot analysis using 125I-goat anti-rabbit IgG, immunoprecipitation of N-type VDCC, and all other general methods have been described in detail (17, 19). The results are expressed as mean ± S.D. Statistical analysis was performed by a paired t test or Mann-Whitney Rank Sum test. p values less than 0.05 were considered significant.

    RESULTS AND DISCUSSION
Top
Abstract
Introduction
Procedures
Results & Discussion
References

beta 4 Isoform Is Not Expressed in lh/lh Mice-- The lh gene mutation was anticipated to lead to truncation of beta 4 to an N-terminal fragment predicted to have a mass of 21 kDa (9). The lh mRNA was detected at levels 20% of the wild-type beta 4 message (9), suggesting the possibility that the lh gene product may be expressed in lh/lh mice. Using beta 4-specific antibodies, we probed forebrain and cerebellar homogenates from lh/lh mice to evaluate the level of expression of full-length beta 4. In contrast to wild-type mice where we detected full-length beta 4 (62 kDa), there was no beta 4 detected in either forebrain or cerebellum from lh/lh mice (Fig. 1). To further investigate expression of the lh gene product, we used an antibody (Ab CW24) raised to amino acids 53-70 in the beta 4 which are also present in all beta  isoforms (16, 17). Ab CW24 identified two populations of high (beta 1b and beta 2) and low (beta 3 and beta 4) molecular weight beta  isoforms previously characterized in rat brain (17). The relative intensity of these bands clearly differed among the lh/lh versus wild-type mouse samples (Fig. 1). However, with the exception of 42-40-kDa proteolytic beta  fragments, there were no detectable Ab CW24-immunoreactive proteins that could be attributed to the predicted 21-kDa product of the lh gene in either lh/lh mouse forebrain or cerebellum. These results suggest that the lh mutation causes a complete loss of beta 4 protein.


View larger version (31K):
[in this window]
[in a new window]
 
Fig. 1.   beta 4 isoform is not detected in forebrain or cerebellum of lh/lh mice. Forebrains and cerebella from lh/lh and wild-type mice were removed, resuspended in 50 mM HEPES, 1 mM EGTA, and protease inhibitors, and homogenized. The samples (150 µg/lane) were resolved by SDS-PAGE on a 12% gel (19), transferred to nitrocellulose, and incubated with affinity-purified antibodies to beta 4 (1/100 dilution) or Ab CW24 (a pan-specific anti-beta antibody, 1/200 dilution) and visualized with enhanced chemiluminescence. Lane 1, lh/lh cerebellum; lane 2, wild-type cerebellum; lane 3, lh/lh forebrain; lane 4, wild-type forebrain.

The Pool of Available beta  Subunits Is Decreased in lh/lh Mice-- To investigate the pool of available beta  isoforms in forebrain and cerebellum of lh/lh and wild-type samples, the level of expression of all beta  isoforms was quantified using a pan-specific anti-beta antibody (Ab CW24) and a panel of beta  isoform-specific antibodies. There are regional differences in expression of beta  isoforms with increased expression of all beta  isoforms (with the exception of the beta 4) in forebrain samples. Significantly, we observed differences in expression among specific beta  isoforms in lh/lh mice compared with wild-type mice. The level of expression of all beta  isoforms as detected by the anti-beta pan-specific antibody is lower in lh/lh forebrain and cerebellum than in wild-type samples (Fig. 2), indicating that the level of total beta  isoforms is not maintained in the lh/lh samples. In both lh/lh forebrain (p < 0.001) and cerebellum (p < 0.05), the level of expression of beta 1b was increased compared with wild-type mice (Fig. 2). In forebrain, the increase in beta 1b expression was greater than 50%. These results are consistent with our previous characterization of beta 1b as an inducible and regulated protein (16, 17). In contrast, differences in the levels of expression of beta 2 and beta 3 in lh/lh versus wild-type mice were not statistically significant in either forebrain or cerebellar samples.


View larger version (25K):
[in this window]
[in a new window]
 
Fig. 2.   Altered level of expression of beta  isoforms in wild-type and lh/lh brain. Forebrains (FB) and cerebella (CB) from lh/lh and wild-type mice were removed, resuspended in 50 mM HEPES, 1 mM EGTA, and protease inhibitors and homogenized. The samples (150 µg/lane) were resolved by SDS-PAGE, transferred to nitrocellulose, and incubated with affinity-purified antibodies pan-specific for all beta  and isoform-specific antibodies to beta 1b, beta 2, beta 3, and beta 4. The amount of beta  was quantified using 125I-IgG. Results obtained were from duplicate blots representing n = 3 wild-type () and 3 lh/lh (black-square) animals for forebrain samples and n = 2 wild-type and 3 lh/lh animals for cerebellar samples; **, p < 0.001 and *, p < 0.05 as determined by a paired t test.

Decreased Expression of N-type VDCC and alpha 1B in lh/lh Compared with Wild-type Mice-- The density of N-type VDCC has been previously shown to be higher in forebrain versus cerebellar samples (21, 23, 24). Furthermore, beta 4 is the predominant isoform associated with VDCC from cerebellum, and beta 3 is the predominant isoform associated with VDCC from forebrain (5, 17, 20, 25). Therefore, these patterns of VDCC subunit expression suggested regional differences in acquisition of functional N-type VDCC in cerebellum and forebrain from lh/lh versus wild-type mice. Using 125I-CTX radioligand binding assays and Scatchard analyses (18) (Fig. 3), we observed a significant decrease (p < 0.05) in expression of N-type VDCC in lh/lh forebrain (1.49 ± 0.41 pmol/mg) compared with wild-type forebrain (2.70 ± 0.63 pmol/mg). There was a single 125I-CTX binding site detected in the forebrain samples with Kd values of approximately 28 pM for both the lh/lh and wild-type samples. The level of alpha 1B expressed in forebrain samples was also quantified (Fig. 3) to examine possible discrepancies between expression of 125I-CTX binding sites and alpha 1B protein (17). Despite the decrease in 125I-CTX binding sites in lh/lh forebrain, similar levels of alpha 1B protein are expressed in forebrain of lh/lh and wild-type mice. These data strongly suggest that expression of alpha 1B protein in forebrains of lh/lh mice is maintained at wild-type levels, while the assembly of alpha 1B into a complex that can support 125I-CTX binding is compromised. The decreased expression of 125I-CTX binding sites in lh/lh forebrain (Fig. 3) may reflect the decreased availability of beta  (Fig. 2) required to traffic alpha 1B to the plasma membrane (26).


View larger version (19K):
[in this window]
[in a new window]
 
Fig. 3.   Differential expression of alpha 1B and N-type VDCC in wild-type and lh/lh mouse brain. Forebrains (FB) and cerebella (CB) from lh/lh and wild-type mice were removed, resuspended in 50 mM HEPES, 1 mM EGTA, and protease inhibitors, and homogenized. The samples (150 µg/lane) were resolved by SDS-PAGE, transferred to nitrocellulose, and incubated with affinity-purified antibodies to alpha 1B subunit (Ab CW14). The amount of alpha 1B was quantified using 125I-IgG. The results obtained were from duplicate blots representing n = 3 wild-type () and 3 lh/lh (black-square) mice for forebrain samples and n = 2 wild-type and 3 lh/lh mice for cerebellar samples; **, p < 0.001, as determined by a paired t test. Scatchard plot analysis of 125I-CTX binding to N-type VDCC in wild-type and lh/lh mouse forebrain and cerebellum was carried out as described (17, 18). The amount of protein per assay was: lh/lh forebrain, 3-5 µg; wild-type forebrain, 2-4 µg; lh/lh cerebellum, 11-20 µg; and wild-type cerebellum, 9-20 µg. The following Kd values were calculated: lh/lh forebrain, 27.8 (± 7.6) pM; wild-type forebrain, 28.4 (± 15.3) pM; lh/lh cerebellum, 75.6 (± 10.0) pM; and wild-type cerebellum, 66.6 (± 5.0) pM. The results obtained were from tissue samples representing n = 4 wild-type and 3 lh/lh animals for forebrain samples and n = 3 wild-type and 3 lh/lh animals for cerebellar samples; *, p < 0.05, as determined by a paired t test.

We also observed decreased expression (p < 0.05) of 125I-CTX binding sites in lh/lh cerebellum (0.32 ± 0.05 pmol/mg) compared with wild-type cerebellum (0.53 ± 0.10 pmol/mg). However, in contrast to the forebrain samples, radioligand binding experiments detected two 125I-CTX binding sites in cerebellum. The high affinity site (Kd values of approximately 70 and 67 pM for the lh/lh and wild-type cerebellar samples, respectively) is characteristic of the N-type VDCC. The low affinity site for 125I-CTX detected in cerebellar samples is likely because of the low affinity binding of 125I-CTX for the P/Q-type VDCC (5) and was not pursued further in these studies. In contrast to lh/lh forebrain, decreased alpha 1B protein is expressed in lh/lh mouse cerebellum, suggesting that expression of alpha 1B protein is not maintained at wild-type levels. It seems reasonable to consider that the loss of the beta 4 from lh/lh cerebellum cannot be entirely compensated despite the increased level of expression of beta 1b (Fig. 2). The decreased expression of N-type VDCC or altered expression of other VDCC in the cerebellum of the lh/lh mouse may be the molecular basis of ataxia associated with the lh/lh phenotype. It should be stated that the level of expression of functional N-type VDCC in sympathetic neurons was also decreased in "beta 3 knock-out mice" (27). However, in contrast to the lh/lh mouse, the "beta 3 knock-out" mouse is phenotypically normal (27). The expression of other beta  isoforms in response to the elimination of beta 3 has not yet been reported.

Increased Incorporation of beta 1b into N-type VDCC of the lh/lh Mouse-- To determine the structural consequences of abnormal beta  isoform expression in lh/lh mice upon N-type VDCC assembly, the endogenous alpha 1B/beta subunit complexes were evaluated in immunoprecipitation assays using anti-alpha 1B, anti-beta generic (Ab CW24), and beta  isoform-specific antibodies (17). The assay conditions were defined such that the pan-specific anti-beta antibody immunoprecipitated a similar fraction of N-type VDCC in all samples (Fig. 4). The relative contribution of beta  isoforms to the N-type VDCC present in forebrain and cerebellum of lh/lh is clearly altered compared with the wild-type mice (Fig. 4). As anticipated from the lack of detectable beta 4 in forebrains from lh/lh mice (Fig. 1), the disparity in the association of beta 4 with N-type VDCC in lh/lh versus wild-type mice was quite dramatic, as antibodies to beta 4 immunoprecipitated less than 10% of the total N-type VDCC solubilized from the cerebellum of lh/lh mouse (Fig. 4). With regard to the N-type VDCC extracted from forebrain, the fraction of N-type VDCC associated with beta 1b was statistically increased in lh/lh versus wild type mice (Fig. 4). In contrast, neither the association of beta 2 nor beta 3 with the N-type VDCC was affected in forebrains of lh/lh versus wild-type mice (Fig. 4). However, although beta 1b was increased in expression in lh/lh cerebellum (Fig. 2), there was no statistically significant increase in incorporation of any beta  isoform into cerebellar N-type VDCC (Fig. 4). It is reasonable to suggest that down-regulation of alpha 1B expression (Fig. 3), rather than increased incorporation of beta 1b into assembled N-type VDCC, is the primary mechanism of compensation in lh/lh cerebellum. Additional studies are required to determine whether the compensatory mechanisms that alter beta subunit composition of the N-type VDCC in the lh/lh mouse influence the expression and assembly of other VDCC.


View larger version (22K):
[in this window]
[in a new window]
 
Fig. 4.   Altered alpha 1B/beta subunit assembly leads to different populations of N-type VDCC in wild-type and lh/lh brain. Forebrains (FB) and cerebella (CB) from lh/lh (black-square) and wild-type () mice were solubilized with 0.75% CHAPS incubated with 125I-CTX (9000-12,000 cpm/assay) for 30 min. Affinity-purified antibodies to the alpha 1B (Ab CW14), pan-specific anti-beta antibodies, and isoform-specific antibodies to beta 1b, beta 2, beta 3, and beta 4 (25 µg/assay) were added for 1 h (17). Protein A-Sepharose 4B was added with constant mixing. 125I-CTX bound to the immunoprecipitated N-type VDCC was recovered in protein A pellets, counted, and normalized to the fraction of 125I-CTX immunoprecipitated by Ab CW14 (17, 19). The approximate amount of total 125I-CTX binding/sample prior to immunoprecipitation was in the range of 1000-1600 specific counts/min of 125I-CTX for the cerebellar samples and 2500-8000 specific counts/min of 125I-CTX for the forebrain samples. Results obtained were from n = 4 wild-type and 4 lh/lh animals carried out in duplicate; *, p < 0.05 and **, p < 0.001 as determined by a paired t test.

Although the specific biophysical properties derived from the population of N-type VDCC present in wild-type and lh/lh forebrain have yet to be determined, it is interesting to note that beta 1b and beta 4 have similar effects upon closed state inactivation of recombinant N-type VDCC (8). Similar kinetic effects of beta 1b and beta 4 suggest tolerance of the beta 1b assembled into N-type VDCC, and this atypical channel composition may explain the absence of the neurodegeneration frequently observed in other epileptic mouse strains (3, 4).

These results are the first to indicate that assembly of the high voltage-activated N-type VDCC is altered in the lh/lh mouse. These findings do not exclude the possibility that the expression of other high voltage-activated VDCC is also effected as beta 4 is associated with mature L-type, N-type, and P/Q-type VDCC (17, 20, 25). However, it is interesting to point out that although low voltage-activated T-type channels have been implicated in the initiation of thalamic seizures in absence epilepsies (28, 29), the T-type alpha 1G and alpha 1H isoforms do not contain consensus beta  binding domains (14, 30), suggesting that T-type VDCC expression, unlike the high voltage-activated VDCC, may not be directly regulated by beta  subunits.

Differential modulation of the N-type VDCC by protein kinases in lh/lh mice is another property that may result from the assembly of beta 1b in place of beta 4. The beta 1b (31) contains consensus sites for protein kinase A modification; conversely in the beta 4, the protein kinase A consensus sites are absent (32). Thus, the inappropriate inclusion of beta 1b into the N-type VDCC complex in the lh/lh mouse in lieu of beta 4 may alter protein kinase-mediated modulation of the channel and thus effect calcium entry and calcium-dependent signaling.

beta Subunit Composition of N-type VDCC Expressed in lh/lh Mice Resembles N-type VDCC Population of Immature (P2) Neurons-- In earlier studies, beta 4 was discriminated from the other beta  isoforms by virtue of its striking increase in expression during development (17, 33). The importance of beta 4 to neuronal functioning is reflected in the epileptic and ataxic phenotype of the lh/lh mice, which stands in contrast to the "beta 3 knock-out" mouse that is phenotypically normal (27). The phenotype of lh/lh mice is evident at postnatal day 15 (10, 11), which is consistent with the loss of beta 4 that is normally increased in expression after P7 in developing rat brain (17). The question now arises as to whether the phenotype of lh/lh mice arises primarily because of the loss of beta 4 or as a result of the increased fractional contribution of beta 1b to N-type VDCC complexes. Our recent report that identifies beta 4 as a marker for N-type VDCC maturation unifies these two possibilities (17). The increased fractional contribution of beta 1b to N-type VDCC complexes and the absence of beta 4 assembled into adult lh/lh N-type VDCC result in a population of N-type VDCC that is strikingly similar to immature (P2) N-type VDCC in beta  subunit composition (17). We propose that the mechanism that promotes absence seizures in lh/lh mice, a form of epilepsy more commonly associated with immature brain (28), may be a consequence of prolonged and inappropriate expression of immature alpha 1/beta complexes.

    ACKNOWLEDGEMENTS

We thank Stefan J. Dubel for technical assistance and preparation of the figures for publication. We also thank Dr. Ben Strowbridge, Dr. J. P. Jin, Dr. Richard Zigmond, and Dr. Stephen Jones for critical discussion of the manuscript.

    FOOTNOTES

* This study was funded in part by the National Institute of Mental Health (to M. W. M.), Life and Health Insurance Medical Research Fund (to M. W. M.), American Heart Association (to M. W. M.), and in part by the National Cancer Institute, Department of Health and Human Services, under contract with ABL (to T. D. C.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

§ Established Investigator of the American Heart Association. To whom correspondence and reprint requests should be addressed: Dept. of Physiology and Biophysics, Case Western Reserve University, School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970. Fax: 216-368-1693; E-mail: mwm4{at}po.cwru.edu.

The abbreviations used are: VDCC, voltage-dependent calcium channel; N-type VDCC, omega -conotoxin-sensitive VDCC; alpha 1B, 230-kDa subunit of the N-type VDCCalpha 2/delta , 160-kDa subunit of N-type VDCCbeta 1-beta 4, 53-85-kDa subunits of N-type VDCC125I-CTX, 125I-labeled Tyr-22-omega -conotoxin GVIACHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonatePAGE, polyacrylamide gel electrophoresisP2, postnatal day 2.
    REFERENCES
Top
Abstract
Introduction
Procedures
Results & Discussion
References

  1. Hosford, D. A., and Wang, Y. (1997) Epilepsia 38, 408-414[Medline] [Order article via Infotrieve]
  2. Noebels, J. L. (1986) Adv. Neurol. 44, 97-113[Medline] [Order article via Infotrieve]
  3. Doyle, J., Ren, X., Lennon, G., and Stubbs, L. (1997) Mamm. Genome 8, 113-120[CrossRef][Medline] [Order article via Infotrieve]
  4. Fletcher, C. F., Lutz, C. M., O'Sullivan, T. N., Shaughnessy, J. D., Hawkes, R., Frankel, W. N., Copeland, N. G., and Jenkins, N. A. (1996) Cell 87, 607-617[Medline] [Order article via Infotrieve]
  5. Liu, H., De Waard, M., Scott, V. E. S., Gurnett, C. A., Lennon, V. A., and Campbell, K. P. (1996) J. Biol. Chem. 271, 13804-13810[Abstract/Free Full Text]
  6. Sander, T., Peters, C., Janz, D., Bianchi, A., Bauer, G., Wienker, T. F., Hildmann, T., Epplen, J. T., and Riess, O. (1998) Epilepsy Res. 29, 115-122[CrossRef][Medline] [Order article via Infotrieve]
  7. Kraus, R. L., Sinnegger, M. J., Glossmann, H., Hering, S., and Striessnig, J. (1998) J. Biol. Chem. 273, 5586-5590[Abstract/Free Full Text]
  8. Patil, P., Brody, D. L., and Yue, D. T. (1998) Neuron 20, 1-20[Medline] [Order article via Infotrieve]
  9. Burgess, D. L., Jones, J. M., Meisler, M. H., and Noebels, J. L. (1997) Cell 88, 385-392[Medline] [Order article via Infotrieve]
  10. Dung, H. C., and Swigart, R. H. (1972) Tex. Rep. Biol. Med. 30, 23-39[Medline] [Order article via Infotrieve]
  11. Dung, H. C., and Swigart, R. H. (1971) Tex. Rep. Biol. Med. 29, 273-288[Medline] [Order article via Infotrieve]
  12. Stevanin, G., Durr, A., David, G., Didierjean, O., Cancel, G., Rivaud, S., Tourbah, A., Warter, J. A., Agid, Y., and Brice, A. (1997) Neurology 49, 1243-1246[Abstract]
  13. Zhuchenko, O., Bailley, J., Bonnen, P., Ashizawa, T., Stockton, D. W., Amos, C., Dobyns, W. B., Subramony, S. H., Zoghni, H. Y., and Lee, C. C. (1997) Nat. Genet. 15, 62-69[Medline] [Order article via Infotrieve]
  14. De Waard, M., Pragnell, M., and Campbell, K. P. (1994) Neuron 13, 495-503[Medline] [Order article via Infotrieve]
  15. McEnery, M. W., Vance, C. L., Begg, C. M., Lee, W. L., Choi, Y., and Dubel, S. J. (1998) J. Bioenerg. Biomembr. 40, in press
  16. McEnery, M. W., Haase, H., Vance, C. L., Dubel, S. J., Morano, I., Copeland, T. D., and Choi, Y. (1997) FEBS Lett. 420, 74-78[CrossRef][Medline] [Order article via Infotrieve]
  17. 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[Abstract/Free Full Text]
  18. McEnery, M. W., Snowman, A. M., Sharp, A. H., Adams, M. E., and Snyder, S. H. (1991) Proc. Natl. Acad. Sci. U. S. A. 88, 11095-11099[Abstract]
  19. Vance, C. L., Begg, C. M., Dubel, S. J., Copeland, T. D., Sönnichsen, F. D., and McEnery, M. W. (1998) Neuroscience, in press
  20. Pichler, M., Cassidy, T. N., Reimer, D., Haase, H., Kraus, R., Ostler, D., and Striessnig, J. (1997) J. Biol. Chem. 272, 13877-13882[Abstract/Free Full Text]
  21. Wagner, J. A., Snowman, A. M., Biswas, A., Olivera, B. M., and Snyder, S. H. (1988) J. Neurosci. 8, 3354-3359[Abstract]
  22. McEnery, M. W. (1993) in Molecular and Cellular Biology of Pharmacological Targets (Glossmann, H., and Striessnig, J., eds), pp. 3-39, Plenum Press, New York
  23. Maeda, N., Wada, K., Yuzaki, M., and Mikoshiba, K. (1989) Brain Res. 489, 21-30[Medline] [Order article via Infotrieve]
  24. Litzinger, M. J., Mouritsen, C. L., Grover, B. B., Esplin, M. S., and Abbott, J. R. (1994) J. Child Neurol. 9, 77-80[Medline] [Order article via Infotrieve]
  25. Scott, V. E., De Waard, M., Liu, H., Gurnett, C. A., Venzke, D. P., Lennon, V. A., and Campbell, K. P. (1996) J. Biol. Chem. 271, 3207-3212[Abstract/Free Full Text]
  26. Brice, N. L., Berrow, N. S., Campbell, V., Page, K. M., Brickley, K., Tedder, I., and Dolphin, A. C. (1997) Eur. J. Neurosci. 9, 749-759[Medline] [Order article via Infotrieve]
  27. Smith, S. M., Namkung, Y., Scheller, R. H., Tsien, R. W., and Shin, H. S. (1998) Biophys. J. 74, 120 (abstr.)
  28. Snead, O. C. (1995) Ann. Neurol. 37, 146-157[Medline] [Order article via Infotrieve]
  29. Coulter, D. A., Huguenard, J. R., and Prince, D. A. (1990) Br. J. Pharmacol. 100, 800-806[Abstract]
  30. Perez-Reyes, E., Cribbs, L. L., Daud, A., Lacerda, A. E., Barclay, J., Williamson, M. P., Fox, M., Rees, M., and Lee, J. H. (1998) Nature 391, 896-900[CrossRef][Medline] [Order article via Infotrieve]
  31. Pragnell, M., Sakamoto, J., Jay, S. D., and Campbell, K. P. (1991) FEBS Lett. 291, 253-258[CrossRef][Medline] [Order article via Infotrieve]
  32. Castellano, A., Wei, X., Birnbaumer, L., and Perez-Reyes, E. (1993) J. Biol. Chem. 268, 12359-12366[Abstract/Free Full Text]
  33. Tanaka, O., Sakagami, H., and Kondo, H. (1995) Brain Res. Mol. Brain Res. 30, 1-16[CrossRef][Medline] [Order article via Infotrieve]


Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.