Abstract
Cardiac voltage-dependent sodium channels (Nav) are drug targets for synthetic inactivation inhibitors typified by (±)-4- [3-(4-diphenylmethyl-1-piperazinyl)-2-hydroxy propoxy]-1H-indole-2-carbonitrile (DPI 201-106), of which the molecular mode of action is not yet defined. The previous observation by Mevissen and coworkers in 2001 of the electrophysiological ineffectiveness of DPI 201-106 in the bovine heart, in contrast to other species, offers the opportunity for investigating these open questions. We now report about the molecular cloning, expression in Xenopus laevis oocytes, and electrophysiological characterization of a unique bovine heart sodium channel. Although the predicted 2022-amino acid bovine heart sodium channel (bH1) shares 92% identity with the rat and human isoforms and normal gating properties, it displays drastically reduced sensitivity to (−)-(S)-6-amino-α-[(4-diphenylmethyl-1-piperazinyl)-methyl]-9H-purine-9-ethanol (SDZ 211-939). Experimental results with Anemonia sulcata toxin II (0.1–2.5 μM) exclude the possibility of an overall insensitivity of this isoform to various sodium channel modulators. The binding of SDZ 211-939 seems to be largely unaffected (EC50 of 10.3 and 10.6 μM for bovine and rat isoforms, respectively) but the corresponding efficacy in bovine (Vm of 0.15) is approximately 5 times smaller compared with the rat heart isoform (Vm of 0.69). The comparison of the primary structure of bH1 to other sodium channels and the gating properties obtained in presence or absence of SDZ 211-939 revealed a high degree of similarity. Whether the mechanism of channel modulation depends on the interaction of synthetic modulators with some possibly voltage-independent part of the inactivation machinery needs to be determined.
Footnotes
-
This research was supported by a grant from the Schmid-Fonds (Prof. Tino Hess).
- Abbreviations:
- DPI 201-106
- (±)-4-[3-(4-diphenylmethyl-1-piperazinyl)-2-hydroxy propoxy]-1H-indole-2-carbonitrile
- TTX
- tetrodotoxin
- bH1
- bovine heart sodium channel
- ATX-II
- Anemonia sulcata (sea anemone) toxin II
- SDZ 211-939
- (−)-(S)-6-amino-α-[(4-diphenylmethyl-1-piperazinyl)-methyl]-9H-purine-9-ethanol
- rH1
- rat heart sodium channel
- PCR
- polymerase chain reaction
- RACE
- rapid amplification of cDNA ends
- GSP
- gene specific
- Nav
- voltage-dependent sodium channel
- MBS
- modified Barth's solution
- bp
- base pair(s)
- UTR
- untranslated region
- I/V
- current-voltage
- Received March 7, 2002.
- Accepted June 6, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|