Atrial L-type Ca2+-channel, beta-adrenorecptor, and 5-hydroxytryptamine type 4 receptor mRNAs in human atrial fibrillation.
Molecular and electrical remodeling of ion channels determining action potential duration has been proposed as a major mechanism in chronic atrial fibrillation. We investigated the mRNA expression of the cardiac L-type Ca2+-channel subunits alpha1c, alpha2/delta1, beta1a, and beta1b/c in atrial tissue of patients with chronic atrial fibrillation compared to patients in sinus rhythm. In addition, the mRNA expression of the 5-hydroxytryptamine type 4-, beta1-, and beta2-adrenergic receptors, which are known to stimulate the L-type Ca2+-current in human atrium, was analyzed and the effect of chronic beta-blocker treatment on the mRNA expression of these receptors and of the L-type Ca2+-channel subunits was assessed. Total RNA was isolated from right atrial appendages of patients in sinus rhythm and of patients with chronic atrial fibrillation. Then, semiquantitative RT-PCR using 18S RNA as the "housekeeping gene" was performed. In patients with chronic atrial fibrillation, there were only mild reductions in mRNA expression of the alpha1c-subunit (-15.5 %, p = 0.13), and of the beta1-subunit isoforms a and c (-13.3 %, p = 0.14 and -16.6%, p = 0.18, respectively). However, mRNA expression of the alpha2/delta1-subunit (-31.5 %, p < 0.01) and of the beta1-subunit isoform b (-39.9 %, p < 0.0005) was significantly reduced in patients with chronic AF. Taken together, the mRNA expression of the beta1-subunit isoforms b and c, which are splice variants, was significantly down-regulated by 26.5 % (p < 0.05) in these patients. The analysis of the beta1c/beta1b ratio resulted in a significant shift by 39.2 % (p < 0.0001) in favor of beta1c in patients with chronic atrial fibrillation. In the AF patients, the abundance of the 5-HT4-receptor transcript was significantly reduced by 36 % (p < 0.05). The beta-adrenoreceptor transcription was unchanged. In both SR and AF patients, chronic beta-blocker treatment did neither significantly effect the mRNA expression of the L-type Ca2+-channel subunits, the beta-adrenoreceptor subtypes 1 and 2, nor that of the 5-HT4-receptor. Our data show that chronic AF is associated with a decrease in the atrial mRNA amount of auxiliary subunits of the L-type Ca2+-channel and of the 5-HT4-receptor. This supports the hypothesis that the observed alterations in mRNA transcription in AF patients may lead to a decrease in the availability of functional L-type Ca2+-channels and 5-HT4-receptors and/or reduce L-type Ca2+-current amplitude and density, thus, promoting and stabilizing the arrhythmia.
Grammer
J B
JB
Deutsches Herzzentrum München, Klinik für Herz- und Gefässchirurgie.
Zeng
X
X
Bosch
R F
RF
Kühlkamp
V
V
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000368:Aged; D001281:Atrial Fibrillation / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics*; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000235:genetics*; D011985:Receptors, Serotonin / Q000235:genetics*
D000319:Adrenergic beta-Antagonists; D020746:Calcium Channels, L-Type; D020033:Protein Isoforms; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D011985:Receptors, Serotonin