©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
A Novel K Channel -Subunit (hKv1.3) Is Produced via Alternative mRNA Splicing (*)

(Received for publication, September 13, 1995; and in revised form, October 2, 1995)

Sarah K. England (1) Victor N. Uebele (2)(§) Jayaveera Kodali (3) Paul B. Bennett (2) (3)(¶) Michael M. Tamkun (1) (2)(**)

From the  (1)Departments of Molecular Physiology and Biophysics, (2)Pharmacology, and (3)Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232

ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS and DISCUSSION
CONCLUSIONS
FOOTNOTES
ACKNOWLEDGEMENTS
REFERENCES

ABSTRACT

Voltage-gated K channels can form multimeric complexes with accessory beta-subunits. We report here a novel K channel beta-subunit cloned from human heart, hKvbeta1.3, that has 74-83% overall identity with previously cloned beta-subunits. Comparison of hKvbeta1.3 with the previously cloned hKvbeta3 and rKvbeta1 proteins indicates that the carboxyl-terminal 328 amino acids are identical, while unique variable length amino termini exist. Analysis of human beta-subunit cDNA and genomic nucleotide sequences confirm that these three beta-subunits are alternatively spliced from a common beta-subunit gene. Co-expression of hKvbeta1.3 in Xenopus oocytes with the delayed rectifier hKv1.5 indicated that hKvbeta1.3 has unique functional effects. This novel beta-subunit induced a time-dependent inactivation during membrane voltage steps to positive potentials, induced a 13-mV hyperpolarizing shift in the activation curve, and slowed deactivation ( = 13 ± 0.5 ms versus 35 ± 1.7 ms at -40 mV). Most notably, hKvbeta1.3 converted the Kv1.5 outwardly rectifying current voltage relationship to one showing strong inward rectification. These data suggest that Kv channel current diversity may arise from association with alternatively spliced Kv beta-subunits. A simplified nomenclature for the K channel beta-subunit subfamilies is suggested.


INTRODUCTION

Voltage-gated K channels (Kv) (^1)are important regulators of membrane action potentials as well as many other cellular functions including maintenance of the resting membrane potential, regulating neuron firing, and secretion(1, 2, 3) . Most tissues contain multiple channel types belonging to one or more Kv gene subfamilies(3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15) . However, assigning specific K channel clones to a native current often is difficult since most heterologously expressed Kv channels display either a fast inactivating or a delayed rectifier type current, often with similar pharmacology. While possible factors contributing to this diversity may include Kv channel glycosylation, phosphorylation, and heterotetrameric alpha-subunit formation within a gene subfamily(16, 17, 18, 19) , recent studies have shown that beta-subunits associate with and functionally alter Kv channel clones in heterologous systems(20, 21, 22, 23, 24, 25, 26) .

At present, four Kv beta-subunits have been reported. Three distinct K channel beta-subunits were cloned from rat brain(21, 27) . The rat Kvbeta1 subunit confers rapid A-type inactivation on the Kv1.1 delayed rectifier channel, while the rat Kvbeta2 isoform does not alter K channel current phenotypes in the Xenopus oocyte expression system(21) . Heinemann and co-workers (27) have reported a third beta-subunit from rat brain originally named Kvbeta3 that shares 68% identity with rKvbeta1 and induces partial inactivation in channels of the Kv1 family. The fourth distinct beta-subunit clone, also termed Kvbeta3, was isolated from human and ferret heart(23, 24, 26) . Identity of this Kvbeta3 to previously cloned beta-subunits is greatest in the carboxyl-terminal region with complete identity of hKvbeta3 and rKvbeta1 in the carboxyl 329 amino acids and 85% identity to rKvbeta2. However, the first 79 amino acids of hKvbeta3 share only 25% identity with rKvbeta1 and do not align with rKvbeta2. Fast inactivation of Kv1.4 was accelerated when expressed with hKvbeta3 (23, 24, 25) and fast inactivation and a 20-mV hyperpolarizing shift in the activation curve was conferred on the delayed rectifier Kv1.5(23, 26) . Human Kvbeta3 has no functional effect on the Kv1.1, Kv1.2, and Kv2.1 channel clones(23) , although these channels have been postulated to associate with accessory subunits(28, 29) .

The complete amino acid identity between rKvbeta1 and hKvbeta3 in the carboxyl terminus suggests that Kv channel beta-subunit isoforms are encoded by a single beta-subunit gene. Alternative splicing was suggested previously (21, 26, 30) since the point of divergence between rKvbeta1 and hKvbeta3 cDNA contained a potential splice junction and the nucleotide sequence identity in the carboxyl terminus was >90%. Calcium channel beta-subunits are encoded by four different genes with alternative splicing of the beta1 and beta2 genes giving rise to multiple beta-subunits within these subfamilies(31, 32) . Cell-specific alternative splicing of Kv beta-subunits may be one mechanism responsible for the diversity of Kv channel current among cell types.

We report here the cloning and characterization of a cDNA from human heart that encodes a unique K channel beta-subunit designated hKvbeta1.3. The hKvbeta1.3 subunit uniquely alters the functional properties of hKv1.5, converting it from a delayed rectifier to a channel with rapid, but partial, inactivation. In addition, this current activates at lower voltages, rectifies at depolarized potentials, and has slowed deactivation. Nucleotide sequence comparison of cDNA and genomic DNA encoding human Kvbeta1.3, Kvbeta3, and Kvbeta1 indicate that these subunits are encoded by a common beta-subunit gene, here designated the Kvbeta1 subfamily gene. We suggest that the nomenclature be changed to reflect that the Kvbeta1 subunit family members are generated through alternative mRNA splicing (Table 1).




EXPERIMENTAL PROCEDURES

Isolation and Characterization of Kvbeta1.3

PCR-generated cDNA fragments corresponding to nucleotides 435 to 1089 of rKvbeta2.1 were used to screen 3.5 times 10^5 amplified recombinants from a gt10 cardiomyopathic human heart ventricular cDNA library using previously described conditions (33) . The primary screening yielded a partial clone (8-82, 3.0 kb) which was subcloned into pBluescript (KS+) via NotI and sequenced using double-stranded templates and appropriate oligonucleotide primers (Sequenase 2.0, United States Biochemical Corp.). This clone lacked an in-frame stop codon 5` to the first ATG, suggesting it did not represent a full-length coding sequence. Repeated efforts to isolate additional 5` sequence from a cDNA library were unsuccessful. To clone the 5` end of 8-82, PCR-generated 260-nucleotide fragments unique to the 5` end of 8-82 were used to screen 4.2 times 10^5 amplified recombinants from a EMBL-3 human genomic library (Clontech). The primary screening yielded one clone that was isolated using Wizard Magic Lambda Preps per the manufacturer's instructions (Promega). This 14-kb clone was digested by SacI/EcoRI, electrophoresed, transferred to nitrocellulose, and hybridized at high stringency(4) . A 4-kb fragment that hybridized to the 260-nucleotide probe was subcloned into pGEM and sequenced. This genomic fragment contained the 26 coding nucleotides missing from the 5` end of 8-82 and contained in-frame stop codons 5` to the ATG. The clone was assembled by linearizing clone 8-82 in pBluescript (KS) with BglII and ligating in a 43-bp fragment containing the 5` end of 8-82. The completed clone was verified by sequencing and referred to as hKvbeta1.3.

Genomic Isolation of hKvbeta1.2 and cDNA Isolation of hKvbeta1.1

PCR-generated cDNA fragments of Kvbeta1.2 (nucleotides -74 to 348) were used to screen 4.2 times 10^5 amplified recombinants from a EMBL-3 human genomic library (Clontech). The primary screening yielded an 13-kb clone that was isolated as described above. This clone was digested with Sau3AI, and fragments of multiple sizes were ligated into the BamHI site of pGEM. A plasmid containing a 1-kb genomic fragment positive for Kvbeta1.2 was selected by colony hybridization and sequenced using appropriate oligonucleotide primers.

Isolation of hKvbeta1.1 cDNA was completed by generating PCR fragments corresponding to nucleotides 1-216 of rKvbeta1 and screening 2.8 times 10^5 unamplified recombinants from a newly constructed ZAPII (Stratagene) cDNA library made from human cerebral cortex mRNA (Clontech). A 4-kb clone was isolated, and plaque-purified clones were recovered by in vivo excision yielding hKvbeta1.1 in pBluescript (SK-). Nucleotide sequence in various regions was determined as described above.

Electrophysiological Recording and Data Analysis

Templates for in vitro cRNA synthesis were prepared by isolating a XbaI/AccI fragment of hKvbeta1.3 (nucleotides -20 to 1520) from pBluescript (KS), blunting the DNA ends with Klenow and ligating into the SmaI site of the modified pSP64T vector (34) . This construct was linearized with EcoRI prior to cRNA synthesis. The hKv1.5 cRNA template was prepared as described previously(35) . Human Kvbeta1.3 and hKv1.5 cRNAs were synthesized using the SP6 mMessage mMachine kit (Ambion) according to the manufacturer's instructions.

Defolliculated Xenopus oocytes were prepared as described previously (19) and injected with approximately 40 nl (4-20 ng) of in vitro transcribed cRNA. These dilutions resulted in peak currents of 1-10 µA. Electrophysiological recordings have been described in detail previously(19, 26) . Oocytes were bathed in an extracellular solution containing 96 mM NaCl, 2 mM KCl, 1.8 mM CaCl(2), 1 mM MgCl(2), 5 mM Hepes (pH 7.5 with NaOH). Membrane currents were recorded using a two-microelectrode voltage clamp amplifier from Warner Instruments (New Haven, CT). Values are expressed as mean ± S.E. unless indicated otherwise. All experiments were performed at room temperature.


RESULTS and DISCUSSION

Cloning and Sequence Analysis

While one potential factor underlying functional diversity of the Kv channels in both brain and heart has been attributed to heteromultimeric formation of various alpha-subunits(16, 17, 18, 19) , other possibilities include association of one or more function-altering beta-subunits. beta-Subunits have been shown to modulate inactivation kinetics, voltage dependence, and current amplitudes of voltage-gated K, Na, and Ca channels (20, 21, 24-26, 32, 36-41), and the voltage and calcium sensitivity of the Ca-activated K channels (42) . In order to understand the relationship between Kv cardiac clones and native currents, it is necessary to identify the possible alpha- and beta-subunit interactions.

Screening an amplified human heart cDNA library at low stringency with a PCR-generated cDNA probe corresponding to nucleotides 435-1089 of rKvbeta2.1 yielded two partial cDNA clones as determined by nucleotide sequencing. The deduced amino acid sequence of one of these clones (hbeta2-1) was found to be nearly identical with rKvbeta2.1 and likely represents the human homologue of this previously cloned rat subunit(21) . The other cDNA (hbeta8-82) was most similar to rKvbeta1.1 but exhibited little amino acid identity within the postulated amino terminus and lacked a likely translation start site. Additional screens of cDNA libraries did not yield a full-length clone. Screening a human genomic library produced the 26 nucleotides missing from the 5` end and an obvious translation start site. The initiating methionine was assigned because it represents the first in-frame ATG positioned 3` of termination codons in an open reading frame encoding a 419-amino acid protein (47 kDa). Hydropathy analysis did not reveal a hydrophobic domain, suggesting that similar to other beta-subunits, hKvbeta1.3 is likely a cytoplasmic protein. An amino acid sequence comparison between hKvbeta1.3, hKvbeta1.2, rKvbeta1.1, and rKvbeta2.1 is illustrated in Fig. 1. The carboxyl-terminal 328 amino acids of hKvbeta1.3 are 100% identical with rKvbeta1.1 and hKvbeta1.2 and share 85% identity with rKvbeta(2). However, the first 91 amino acids of hKvbeta1.3 share <10% identity with hKvbeta1.2, rKvbeta1.1, and rKvbeta2.1.


Figure 1: Comparison of hKvbeta1.3, hKvbeta1.2, rKvbeta1.1, and rKvbeta2.1 amino acid sequences. Identical amino acid residues are indicated by dashes. The rKvbeta1.1, hKvbeta1.2, and rKvbeta2.1 sequences are from Refs. 21, 23 and 26.



To determine whether hKvbeta1.3 and hKvbeta1.2 represent splice variants of the same gene, 3`-untranslated regions were compared. Alignments of this 1800-base pair region showed 99% nucleotide identity between clones isolated from separate individuals, suggesting that hKvbeta1.3 and hKvbeta1.2 represent splice variants with minor allelic differences. To confirm that Kvbeta1.1 is also derived from this gene, Kvbeta1.1 was cloned from a human cerebral cortex cDNA library. Three different regions from the 3`-untranslated region corresponding to 250, 750, and 1500 bp 3` of the translation stop codon were sequenced and showed complete identity with Kvbeta1.2 and Kvbeta1.3 in this 3`-untranslated region suggesting that all three beta-subunits are encoded by this gene. To confirm the splice junction, we attempted to clone the entire Kvbeta1 gene from a human genomic library by screening with a probe corresponding to the carboxyl-terminal 328 amino acids of Kvbeta1.1. Although several clones were 10-20 kb in length, a full-length gene was not isolated based on the finding that no single clone hybridized to either hKvbeta1.2 or hKvbeta1.3 amino-terminal specific probes. Likewise, when the unique amino termini of hKvbeta1.3 and hKvbeta1.2 were used to isolate additional genomic clones, these clones did not hybridize to the carboxyl-terminal probe. The complete gene encoding the hKvbeta1 subfamily likely exceeds 40 kb.

Fig. 2illustrates the genomic sequences of Kvbeta1.2 and Kvbeta1.3 surrounding the predicted splice site. Both Kvbeta1.2 and Kvbeta1.3 genomic sequences correspond to their respective cDNA in the region marked exon. Both genomic clones contain a consensus sequence for donor/acceptor splice sites as shown by the underlined sequence(43) . These data provide further evidence that at least three beta-subunits result from alternative splicing. Therefore, differential regulation of Kv beta-subunit expression and alternative splicing are likely to be two mechanisms regulating Kv channel diversity. Further in situ analysis and antibody-based immunohistochemical localization of the Kv beta-subunits will further our understanding of Kv channel alpha- and beta-subunit association.


Figure 2: Comparison of hKvbeta1.3 and hKvbeta1.2 genomic sequences surrounding the proposed splice junction. Genomic sequences corresponding to the variable amino termini cDNA sequences of hKvbeta1.3 and hKvbeta1.2 are shown. Genomic and cDNA sequences match in the region marked exon and diverge at the exon/intron border. Consensus splice site sequences are indicated by the underlining(43) .



Functional Expression of hKvbeta1.3

Fig. 3illustrates the effects of Kvbeta1.3 on hKv1.5 currents. Current tracings were obtained during voltage clamp steps to depolarizing membrane potentials where outward current is activated and tail currents are measured during channel deactivation upon steps to -40 mV. Human Kv1.5 normally displays a modest degree of outward rectification and begins to activate at a membrane potential of about -30 mV (Fig. 3A)(44) . In the presence of Kvbeta1.3, Kv1.5 current displays a time-dependent decay or partial inactivation at large depolarizing steps (Fig. 3B) that occurs only at membrane potentials greater than approximately 0 mV. Fig. 3B illustrates also the slower rate of channel deactivation seen in the presence of Kvbeta1.3 relative to the Kv1.5 alone. These deactivating tail currents were best fit by one exponential with time constants of 13.2 ± 0.5 ms for wild-type Kv1.5 and time constants of 34.9 ± 1.7 ms in the presence of Kvbeta1.3 at -40 mV (p < 0.05). Due to the effect of the hKvbeta1.3 which decreases current at larger membrane potentials, the magnitude of the tails may be underestimated. Time constants for the apparent inactivation induced by Kvbeta1.3 were 8.9 ± 0.3 ms at +50 mV and 9.2 ± 0.45 ms at +30 mV (n = 12) (p > 0.1, not significant). Fits of the decay at less positive potentials were less reliable and were not done.


Figure 3: Functional effects of hKvbeta1.3 on hKv1.5. Whole cell potassium current was recorded from Xenopus oocytes expressing hKv1.5 in the absence (A) and presence (B) of hKvbeta1.3, and each cell was normalized to peak current at +50 mV (= 1). The cells were voltage-clamped at a holding potential of -80 mV for 30 s prior to a variable test potential (shown as inset voltage protocol) and then stepped to -40 mV to record deactivating tail currents. In A, the test step was 75 ms in duration which allowed steady state current levels to be attained at each potential. This duration was increased to 100 ms in the presence of the hKvbeta1.3 subunit (B) to permit steady state to be achieved. Normalized tail currents of hKv1.5 in the presence (closed circles) and the absence (closed squares) of hKvbeta1.3 are plotted as a function of test step potential (C). D represents the steady-state current-voltage relationship for Kv1.5 alone (open squares) and Kv1.5 coexpressed with hKvbeta1.3 (open circles). Potassium current was measured at steady state (see open symbols in A and B) and plotted as a function of the test potential. In order to compare different cells, the current was normalized by dividing the current at each membrane potential by the value measured at 0 mV (= 1). Note that hKvbeta1.3 causes an apparent rectification and that the channels begin to open at more negative membrane potentials compared to Kv1.5 alone. Symbols represent between 5 and 10 observations and are plotted as the mean ± 2 times S.E.



An additional effect observed during co-expression of Kv1.5 with Kvbeta1.3 was that the threshold for Kv1.5 channel activation occurred at more negative potentials. The shift in the activation curve toward more negative potentials is illustrated in Fig. 3C where the amplitude of the tail currents is plotted as a function of the membrane potential. Since the driving force is constant during this measurement, the curve reflects the fraction of channels open at each membrane potential. The average midpoint of the activation curve for the hKv1.5 was -7.1 ± 0.5 mV (n = 6) whereas in the presence of the hKvbeta1.3 it was -20 ± 0.5 mV (n = 6). Fig. 3D shows steady state outward current measured during depolarizing steps. Note that hKv1.5 current is observed at more negative potentials when hKvbeta1.3 is present, even at potentials that do not show apparent inactivation (i.e. -20 mV). At membrane potentials greater than approximately 0 mV, hKv1.5 current in the presence of hKvbeta1.3 is suppressed relative to the Kv1.5 alone, thereby converting this apparent outwardly rectifying current voltage relationship to one that shows inward rectification. Future detailed analysis of these interactions will elucidate the underlying effects of hKvbeta1.3.


CONCLUSIONS

Discovery of the novel Kvbeta1.3 subunit and that alternative mRNA splicing generates multiple function altering beta-subunits further complicates determination of the relationship between cardiac clones and native currents. Future cell-specific localization and co-purification studies using Kv beta-antibodies will enable us to understand both the pattern of Kv beta-subunit isoform expression and the Kv channels with which these subunits associate. In addition, analysis of the mechanisms by which Kvbeta1.3 alters the voltage sensitivity, inactivation, and rectification of Kv1.5 will advance our understanding of Kv channel function.


FOOTNOTES

*
This research was supported by National Science Foundation Fellowship BIR-9406860 (to S. K. E.), HL 49330 (to M. M. T.), and HL 46681 (to M. M. T. and P. B. B.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked ``advertisement'' in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank(TM)/EMBL Data Bank with accession number(s) L47665[GenBank].

§
Supported by National Institutes of Health Training Grants GM 07628 and HL 07411-16.

Established Investigator of the American Heart Association.

**
Established Investigator of the American Heart Association. To whom correspondence and reprint requests should be addressed: Dept. of Molecular Physiology and Biophysics, Rm. 724 Medical Research Building, Vanderbilt University Medical Center, 21st and Garland, Nashville, TN 37232-0615. Tel.: 615-322-7009; Fax: 615-322-7236.

(^1)
The abbreviations used are: Kv, voltage-gated K channels; PCR, polymerase chain reaction; kb, kilobase(s).


ACKNOWLEDGEMENTS

We thank Holly Shear, Ian Hopkirk, and Brady Palmer for their excellent technical assistance.


REFERENCES

  1. Rudy, B. (1988) Neuroscience 25, 729-749 [CrossRef][Medline] [Order article via Infotrieve]
  2. Hille, B. (1992) Ionic Channels of Excitable Membranes , 2nd Ed, Sinauer Associates Inc., Sunderland, MA
  3. Sakmann, B., and Trube, G. (1984) J. Physiol. (Lond.) 347, 641-657 [Abstract]
  4. Roberds, S. L., and Tamkun, M. M. (1991) Proc. Natl. Acad. Sci. U. S. A. 88, 1798-1802 [Abstract]
  5. Chandy, K. G., and Gutman, G. A. (1995) in Handbook of Receptors and Channels: Ligand- and Voltage-gated Ion Channels (North, R. A., ed) pp. 1-71, Boca Raton, FL
  6. Hume, J. R., and Uehara, A. (1985) J. Physiol. (Lond.) 368, 525-544 [Abstract]
  7. Heidbuchel, H., Vereecke, J., and Carmeliet, E. E. (1990) Circ. Res. 66, 1277-1286 [Abstract]
  8. Sanguinetti, M. C., and Jurkiewicz, N. K. (1990) J. Gen. Physiol. 96, 195-215 [Abstract]
  9. Sanguinetti, M. C., and Jurkiewicz, N. K. (1991) Am. J. Physiol. 260, H393-H399
  10. Balser, J. R., Bennett, P. B., and Roden, D. (1990) J. Gen. Physiol. 96, 835-863 [Abstract]
  11. Yue, D. T., and Marban, E. (1988) Pfluegers Arch. 413, 127-133 [Medline] [Order article via Infotrieve]
  12. Boyle, W. A., and Nerbonne, J. M. (1991) Am. J. Physiol. 260, H1236-H1247
  13. Benndorf, K., Markwardt, F., and Nilius, B. (1987) Pfluegers Arch. 413, 127-133
  14. Tseng, G. N., and Hoffman, B. F. (1989) Circ. Res. 64, 633-647 [Abstract]
  15. Escande, D., Coulombe, A., and Faivre, J. (1985) Am. J. Physiol. 252, H142-H148
  16. Ruppersberg, J. P., Schroter, K. H., Sakmann, B., Stocker, M., Sewing, S., and Pongs, O. (1990) Nature 345, 535-537 [CrossRef][Medline] [Order article via Infotrieve]
  17. Christie, M. J., North, R. A., Osborne, P. B., Douglass, J., and Adelman, J. P. (1990) Neuron 4, 405-411 [Medline] [Order article via Infotrieve]
  18. Isacoff, E. Y., Jan, Y. N., and Jan, L. Y. (1990) Nature 345, 530-534 [CrossRef][Medline] [Order article via Infotrieve]
  19. Po, S. S., Roberds, S. L., Snyders, D. J., Tamkun, M. M., and Bennett, P. B. (1993) Circ. Res. 72, 1326-1336 [Abstract]
  20. Chouinard, S. W., Wilson, G. F., Schlimgen, A. K., and Ganetzky, B. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 6763-6767 [Abstract]
  21. Rettig, J., Heinemann, S. H., Wunder, F., Lorra, C., Parcej, D. N., Dolly, J. O., and Pongs, O. (1994) Nature 369, 289-294 [CrossRef][Medline] [Order article via Infotrieve]
  22. Scott, V. E., Rettig, J., Parcej, D. N., Keen, J. N., Findlay, J. B., Pongs, O., and Dolly, J. O. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 1637-1641 [Abstract]
  23. Majumder, K., De Biasi, M., Wang, Z., and Wible, B. A. (1995) FEBS Lett. 361, 13-16 [CrossRef][Medline] [Order article via Infotrieve]
  24. Morales, M. J., Castellino, R. C., Crews, A. L., Rasmusson, R. L., and Strauss, H. C. (1995) J. Biol. Chem. 270, 6272-6277 [Abstract/Free Full Text]
  25. Castellino, R. C., Morales, M. J., Strauss, H. C., and Rasmussen, R. L. (1995) Am. J. Physiol. 38, H385-H391
  26. England, S. K., Uebele, V. N., Shear, H., Kodali, J., Bennett, P. B., and Tamkun, M. M. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 6309-6313 [Abstract]
  27. Heinemann, S. H., Rettig, J., and Pongs, O. (1995) Biophys. J. 68, A361
  28. Rehm, H., and Lazdunski, M. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 4919-4923 [Abstract]
  29. Trimmer, J. S. (1991) Proc. Natl. Acad. Sci. U. S. A. 88, 10764-10768 [Abstract]
  30. McCormack, K., McCormack, T., Tanouye, M., Rudy, B., and Stuhmer, W. (1995) FEBS Lett. 370, 32-36 [CrossRef][Medline] [Order article via Infotrieve]
  31. Powers, P. A., Liu, S., Hogan, K., and Gregg, R. G. (1992) J. Biol. Chem. 267, 22967-22972 [Abstract/Free Full Text]
  32. Isom, L. L., De Jongh, K. S., and Catterall, W. A. (1994) Neuron 12, 1183-1194 [Medline] [Order article via Infotrieve]
  33. Tamkun, M. M., Knoth, K., Walbridge, J. A., Kroemer, H., Roden, D., and Glover, D. (1991) FASEB J. 5, 331-337 [Abstract/Free Full Text]
  34. White, M. M., Chen, L., Kleinfield, R., Kallen, R. G., and Barchi, R. L. (1991) Mol. Pharmacol. 39, 604-608 [Abstract]
  35. Po, S. S., Snyders, D. J., Baker, R., Tamkun, M. M., and Bennett, P. B. (1992) Circ. Res 71, 732-736 [Abstract]
  36. De Waard, M., Pragnell, M., and Campbell, K. P. (1994) Neuron 13, 495-503 [Medline] [Order article via Infotrieve]
  37. Messner, D. J., Feller, D. J., Scheuer, T., and Catterall, W. A. (1986) J. Biol. Chem. 261, 14882-14890 [Abstract/Free Full Text]
  38. Messner, D. J., and Catterall, W. A. (1986) J. Biol. Chem. 261, 14882-14890 [Abstract/Free Full Text]
  39. McHugh-Sutkowski, E., and Catterall, W. A. (1990) J. Biol. Chem. 265, 12393-12399 [Abstract/Free Full Text]
  40. Makita, N., Bennett, P. B., and George, A. L. (1994) J. Biol. Chem. 269, 7571-7578 [Abstract/Free Full Text]
  41. Bennett, P. B., Makita, N., and George, A. L. (1993) FEBS Lett. 326, 21-24 [CrossRef][Medline] [Order article via Infotrieve]
  42. McManus, O. B., Helms, L. M. H., Pallanck, L., Ganetzky, B., Swanson, R., and Leonard, R. J. (1995) Neuron 14, 645-650 [Medline] [Order article via Infotrieve]
  43. Mount, S. M. (1982) Nucleic Acids Res. 10, 459-472 [Abstract]
  44. Snyders, D. J., Tamkun, M. M., and Bennett, P. B. (1993) J. Gen. Physiol. 101, 513-543 [Abstract]

©1995 by The American Society for Biochemistry and Molecular Biology, Inc.