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Constitutive overexpression of muscarinic receptors leads to vagal hyperreactivity.

Livolsi A, Niederhoffer N, Dali-Youcef N, Mokni W, Olexa-Zorn C, Gies JP, Marcellin L, Feldman J, Bousquet P - PLoS ONE (2010)

Bottom Line: Sequencing of the coding fragment of the M(2) receptor gene revealed a single nucleotide mutation in 83% of hyperreactive animals, possibly contributing for the transcript overexpression.This phenomenon might represent a compensatory consequence of muscarinic receptors overexpression.The results suggest that cardiac muscarinic receptor overexpression plays a critical role in the development of vagal hyperreactivity, whereas AchE hyperactivity appears as a compensatory consequence of it.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Neurobiologie et Pharmacologie Cardiovasculaire (EA 4438), Université de Strasbourg, Strasbourg, France.

ABSTRACT

Background: Alterations in muscarinic receptor expression and acetylcholinesterase (AchE) activity have been observed in tissues from Sudden Infant Death Syndrome (SIDS). Vagal overactivity has been proposed as a possible cause of SIDS as well as of vasovagal syncopes. The aim of the present study was to seek whether muscarinic receptor overexpression may be the underlying mechanism of vagal hyperreactivity. Rabbits with marked vagal pauses following injection of phenylephrine were selected and crossed to obtain a vagal hyperreactive strain. The density of cardiac muscarinic receptors and acetylcholinesterase (AchE) gene expression were assessed. Blood markers of the observed cardiac abnormalities were also sought.

Methodology/principal findings: Cardiac muscarinic M(2) and M(3) receptors were overexpressed in hyperreactive rabbits compared to control animals (2.3-fold and 2.5-fold, respectively) and the severity of the phenylephrine-induced bradycardia was correlated with their densities. A similar overexpression of M(2) receptors was observed in peripheral mononuclear white blood cells, suggesting that cardiac M(2) receptor expression can be inferred with high confidence from measurements in blood cells. Sequencing of the coding fragment of the M(2) receptor gene revealed a single nucleotide mutation in 83% of hyperreactive animals, possibly contributing for the transcript overexpression. Significant increases in AchE expression and activity were also assessed (AchE mRNA amplification ratio of 3.6 versus normal rabbits). This phenomenon might represent a compensatory consequence of muscarinic receptors overexpression. Alterations in M(2) receptor and AchE expression occurred between the 5th and the 7th week of age, a critical period also characterized by a higher mortality rate of hyperreactive rabbits (52% in H rabbits versus 13% in normal rabbits) and preceeded the appearance of functional disorders.

Conclusions/significance: The results suggest that cardiac muscarinic receptor overexpression plays a critical role in the development of vagal hyperreactivity, whereas AchE hyperactivity appears as a compensatory consequence of it. Since similar vagal disorders were observed recently by us in SIDS, muscarinic receptor overexpression could become a marker of risk of vasovagal syncopes and SIDS.

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Polymorphism of the M2 cholinergic muscarinic receptor gene of normal (N) and vagal hyperreactive (H) rabbits.(a) DNA sequence analysis of the coding fragment of the M2 muscarinic receptor gene (Chmr2) showing the normal CCT codon and the single nucleotide substitution at position 1311 (G instead of T). (b) The severity of vagal pauses was evaluated in conscious animals by measuring the duration of R-R interval on the ECG recording after challenge with PNE 500 µg kg−1 following the procedure described in Material and Methods. DNA sequence analysis of the coding fragment of the M2 muscarinic receptor gene was carried out as described in Material and Methods. Each symbol represents one animal.
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pone-0015618-g006: Polymorphism of the M2 cholinergic muscarinic receptor gene of normal (N) and vagal hyperreactive (H) rabbits.(a) DNA sequence analysis of the coding fragment of the M2 muscarinic receptor gene (Chmr2) showing the normal CCT codon and the single nucleotide substitution at position 1311 (G instead of T). (b) The severity of vagal pauses was evaluated in conscious animals by measuring the duration of R-R interval on the ECG recording after challenge with PNE 500 µg kg−1 following the procedure described in Material and Methods. DNA sequence analysis of the coding fragment of the M2 muscarinic receptor gene was carried out as described in Material and Methods. Each symbol represents one animal.

Mentions: After sequencing the cholinergic receptor M2 gene, we detected a single nucleotide mutation from thymine to guanine (T→G) in position 1311 (Fig. 6a). This mutation transformed the normal CCT codon into CCG, both encoding for the proline amino-acid. The two codons were not equally distributed among animals. Over the 46 rabbits tested, 17 had the wild genotype CCT/CCT, 12 were heterozygous CCT/CCG and 17 were homozygous CCG/CCG. None of the 11 normal rabbits had the mutation, while it was present in 29/35, i.e., 83% of the vagal hyperreactive rabbits (Fig. 6b). The mean R-R interval in normal rabbits was 3318±1336 ms; mean R-R intervals in hyperreactive rabbits were 24700±6855 ms (wild genotype CCT/CCT), 16650±6572 ms (heterozygous CCT/CCG) and 21096±7759 ms (homozygous CCG/CCG) (Fig. 6b).


Constitutive overexpression of muscarinic receptors leads to vagal hyperreactivity.

Livolsi A, Niederhoffer N, Dali-Youcef N, Mokni W, Olexa-Zorn C, Gies JP, Marcellin L, Feldman J, Bousquet P - PLoS ONE (2010)

Polymorphism of the M2 cholinergic muscarinic receptor gene of normal (N) and vagal hyperreactive (H) rabbits.(a) DNA sequence analysis of the coding fragment of the M2 muscarinic receptor gene (Chmr2) showing the normal CCT codon and the single nucleotide substitution at position 1311 (G instead of T). (b) The severity of vagal pauses was evaluated in conscious animals by measuring the duration of R-R interval on the ECG recording after challenge with PNE 500 µg kg−1 following the procedure described in Material and Methods. DNA sequence analysis of the coding fragment of the M2 muscarinic receptor gene was carried out as described in Material and Methods. Each symbol represents one animal.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3008725&req=5

pone-0015618-g006: Polymorphism of the M2 cholinergic muscarinic receptor gene of normal (N) and vagal hyperreactive (H) rabbits.(a) DNA sequence analysis of the coding fragment of the M2 muscarinic receptor gene (Chmr2) showing the normal CCT codon and the single nucleotide substitution at position 1311 (G instead of T). (b) The severity of vagal pauses was evaluated in conscious animals by measuring the duration of R-R interval on the ECG recording after challenge with PNE 500 µg kg−1 following the procedure described in Material and Methods. DNA sequence analysis of the coding fragment of the M2 muscarinic receptor gene was carried out as described in Material and Methods. Each symbol represents one animal.
Mentions: After sequencing the cholinergic receptor M2 gene, we detected a single nucleotide mutation from thymine to guanine (T→G) in position 1311 (Fig. 6a). This mutation transformed the normal CCT codon into CCG, both encoding for the proline amino-acid. The two codons were not equally distributed among animals. Over the 46 rabbits tested, 17 had the wild genotype CCT/CCT, 12 were heterozygous CCT/CCG and 17 were homozygous CCG/CCG. None of the 11 normal rabbits had the mutation, while it was present in 29/35, i.e., 83% of the vagal hyperreactive rabbits (Fig. 6b). The mean R-R interval in normal rabbits was 3318±1336 ms; mean R-R intervals in hyperreactive rabbits were 24700±6855 ms (wild genotype CCT/CCT), 16650±6572 ms (heterozygous CCT/CCG) and 21096±7759 ms (homozygous CCG/CCG) (Fig. 6b).

Bottom Line: Sequencing of the coding fragment of the M(2) receptor gene revealed a single nucleotide mutation in 83% of hyperreactive animals, possibly contributing for the transcript overexpression.This phenomenon might represent a compensatory consequence of muscarinic receptors overexpression.The results suggest that cardiac muscarinic receptor overexpression plays a critical role in the development of vagal hyperreactivity, whereas AchE hyperactivity appears as a compensatory consequence of it.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Neurobiologie et Pharmacologie Cardiovasculaire (EA 4438), Université de Strasbourg, Strasbourg, France.

ABSTRACT

Background: Alterations in muscarinic receptor expression and acetylcholinesterase (AchE) activity have been observed in tissues from Sudden Infant Death Syndrome (SIDS). Vagal overactivity has been proposed as a possible cause of SIDS as well as of vasovagal syncopes. The aim of the present study was to seek whether muscarinic receptor overexpression may be the underlying mechanism of vagal hyperreactivity. Rabbits with marked vagal pauses following injection of phenylephrine were selected and crossed to obtain a vagal hyperreactive strain. The density of cardiac muscarinic receptors and acetylcholinesterase (AchE) gene expression were assessed. Blood markers of the observed cardiac abnormalities were also sought.

Methodology/principal findings: Cardiac muscarinic M(2) and M(3) receptors were overexpressed in hyperreactive rabbits compared to control animals (2.3-fold and 2.5-fold, respectively) and the severity of the phenylephrine-induced bradycardia was correlated with their densities. A similar overexpression of M(2) receptors was observed in peripheral mononuclear white blood cells, suggesting that cardiac M(2) receptor expression can be inferred with high confidence from measurements in blood cells. Sequencing of the coding fragment of the M(2) receptor gene revealed a single nucleotide mutation in 83% of hyperreactive animals, possibly contributing for the transcript overexpression. Significant increases in AchE expression and activity were also assessed (AchE mRNA amplification ratio of 3.6 versus normal rabbits). This phenomenon might represent a compensatory consequence of muscarinic receptors overexpression. Alterations in M(2) receptor and AchE expression occurred between the 5th and the 7th week of age, a critical period also characterized by a higher mortality rate of hyperreactive rabbits (52% in H rabbits versus 13% in normal rabbits) and preceeded the appearance of functional disorders.

Conclusions/significance: The results suggest that cardiac muscarinic receptor overexpression plays a critical role in the development of vagal hyperreactivity, whereas AchE hyperactivity appears as a compensatory consequence of it. Since similar vagal disorders were observed recently by us in SIDS, muscarinic receptor overexpression could become a marker of risk of vasovagal syncopes and SIDS.

Show MeSH
Related in: MedlinePlus