Volume 9 Supplement 1

4th International Conference of cGMP Generators, Effectors and Therapeutic Implications

Open Access

Blockade of CNG channels abrogates urethral relaxation induced by soluble guanylate cyclase activation

  • Domingo Triguero1Email author,
  • Maria Sancho1,
  • Marta García-Flores1 and
  • Ángeles García-Pascual1
BMC Pharmacology20099(Suppl 1):P69

https://doi.org/10.1186/1471-2210-9-S1-P69

Published: 11 August 2009

In the present study, we have characterized the presence and distribution of cGMP-gated cationic channels (CNG) in the rat urethra as well as its putative role in the mediation of the nitrergic relaxation. Previous studies have shown the inhibition of the sheep urethral nitrergic relaxations by the CNG's inhibitor L-cis-diltiazem [1]. Also in the rat urethra, L-cis-diltiazem (50 μM) inhibited nitrergic relaxations elicited by electrical field stimulation (EFS) of arginine-vasopresin (AVP)-precontracted urethral preparations (Figure 1A).
Figure 1

The presence of L-cis-diltiazem (50 μM) rapidly and effectively inhibited relaxation in arginine-vasopresin (AVP)-precontracted urethral preparations induced by both A) EFS (0.8 ms, 10 Hz, 5 s at 2 min-intervals) and B) guanylate cyclase activation by YC-1 (50 μM).

This effect was stereoselective since the isomer D-cis-diltiazem did not have any effect on urethral relaxations. Similarly, L-cis-diltiazem (50 μM) showed a complete blockade of the relaxation induced by the addition of YC-1 (50 μM), an specific activator of the soluble guanylate cyclase (sGC) (Figure 1B), thus reinforcing that L-cis-diltiazem would be acting as specific inhibitor of CNG channels in this tissue.

The presence of these channels in urethral tissue was tested by carrying out conventional RT-PCR studies using retina as a positive control. A band of the predicted size showing after sequencing, a 99% identity with the rod-type CNGA1, together to a second band with a similar size to that ofthe CNGB1 fragment, were obtained. These results suggest that they are heteromeric retina-like CNG channels.

Immunofluorescence studies were performed to analyze the distribution of CNG immunoreactivity (-ir) in sections of the urethral wall. As can be seen in Figure 2, a strong CNG-ir was present in a subpopulation of vimentin-ir cells known as Interstitial Cells of Cajal (ICC), while a fainter labeling was observed in smooth muscle cells (identified by actin-ir). CNG-ir was never observed in neural structures, nerve terminals, nerve trunks or ganglia. This pattern of CNG labeling and co-localization is similar to that described for the cGMP-ir found in the urethra upon functional nitrergic stimulation [2]. We suggest that CNG channels could be an essential ionic mechanism that would link activation of the NOS-GC pathway to relaxation. In addition, these results point to ICC as key elements in the mediation of the nitrergic urethral relaxation, although its precise role remains to be elucidated.
Figure 2

Section of rat urethra showing immunofluorescence for CNG1 channels (green) and vimentin (red) and its co-localization in a intramuscular Interstitial cell [nuclei are stained with DAPI (blue)]. Scale bar: 20 μm.

Declarations

Acknowledgements

This work was supported by a grant (BFU2006-15135-C02-01) from the Ministerio de Educación y Ciencia of Spain.

Authors’ Affiliations

(1)
Department of Physiology, Veterinary School, Complutense University

References

  1. Triguero D, González M, García-Pascual A, Costa G: Atypical relaxation by scorpion venom in the lamb urethral smooth muscle involves both NO-dependent and -independent responses. Naunyn-Schmiedeberg's Arch Pharmacol. 2003, 361: 151-159. 10.1007/s00210-003-0790-8.View ArticleGoogle Scholar
  2. García-Pascual A, Sancho M, Costa G, Triguero D: Interstitial cells of Cajal in the urethra are cGMP-mediated targets of nitrergic neurotransmission. Am J Physiol Renal Physiol. 2008, 295: F971-F983. 10.1152/ajprenal.90301.2008.View ArticlePubMedGoogle Scholar

Copyright

© Triguero et al; licensee BioMed Central Ltd. 2009

This article is published under license to BioMed Central Ltd.

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