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Application of RT-PCR to regional mapping of B1- and B2-adrenergic receptor mRNAs in rat heart.

Toraason-M; Bourgeois-F; Hardouin-S; Oubenaissa-A; Swynghedauw-B; Moalic-JM
Toxicologist 1996 Mar; 30(1)(Part 2):270
Chronotropic and inotropic activities of the heart are stimulated through B1- and B2- adrenergic receptors (AR). Regional distribution of B-ARs and corresponding mRNAs in the heart are not well defined despite the potential for molecular phenotypic redistribution to be a factor in pathological conditions. Investigating regional distribution of specific mRNAs in the rat have been hampered by the paucity of tissue and the low abundance in heart of B-ARs. Reverse transcription in combination with the polymerase chain reaction (RT-PCR) was used to measure the number of B1- and B2-AR Mrna molecules in the four chambers of rat heart. The right atria was microdissected into four sections with the SA node limited to subsection RA/1. RT-PCR resulted in single amplification products of expected sizes. cRNAs specific for B1- and B2-ARs but with restriction sites produced by punctual mutations were used as internal standards. The mean number of B1-AR mRNA molecules per ng of total RNA ranged from 663 +/- 75 to 918 +/- 90 in the ventricular and atrial regions. There was significantly more B1-AR mRNA in right atria than left atria or ventricles. Right atrial subsections RA/1 and RA/2 contained significantly more B1-AR mRNA than subsections RA/3 and RA/4. The number of B2/AR mRNA molecules ranged from 375 +/- 67 to 481 +/- 104 in the regions examined. The number of B2-AR mRNA molecules did not differ significantly among the chambers or subsections. The sums of B1- and B2-AR mRNAs among the individual chambers and atrial subsections were equivalent, but the B1/B2-AR mRNA ratios ranged from 1.45 +/- 0.08 to 2.49 +/- 0.22 and varied significantly. The highest ratio occurred in the right atria and the lowest in left ventricle. Within the right atria, subsection RA/1 exhibited the highest ratio which was significantly greater than subsection RA/3, but not subsections RA/2 or RA/4. Comparison of the above variables between adult (3 mo) and senescent (24 mo) rats revealed significant phenotypic remodeling of B-AR mRNA distribution throughout the myocardium. These changes could contribute to increased rhythm disturbances observed in senescent heart.
Laboratory-animals; Animals; Animal-studies; Heart; Heart-rate; Genes; Cardiovascular-system
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The Toxicologist. Society of Toxicology 35th Annual Meeting, March 10-14,1996, Anaheim, California