© 2002 by European Society of Cardiology
Copyright © 2002, European Society of Cardiology
Expression, regulation and role of the MAGUK protein SAP-97 in human atrial myocardium
aINSERM Unité 460, Faculté de Médecine Xavier Bichat, 16 rue Henri Huchard, 75018 Paris, France
bCNRS-ESA 8078, Hôpital Marie Lannelongue, Le Plessis Robinson, France
cService de Chirurgie Cardiaque, Hôpital Xavier Bichat, Paris, France
* Corresponding author. Tel.: +33-1-44-856-155; fax: +33-1-44-856-157 hatem{at}bichat.inserm.fr
Objective: In various cell types, membrane-associated guanylate kinases proteins called MAGUK play a major role in the spatial localization and clustering of ion channels. Here, we studied the expression and role of these anchoring proteins in human right atrial myocardium by means of various molecular, biochemical and physiological methods. Methods and results: SAP-97, PSD-95, Chapsyn and SAP-102 messengers were detected by reverse transcriptase–polymerase chain reaction (RT-PCR) on mRNA extracted from both whole myocardium and isolated myocytes. Western blot revealed that the MAGUK protein SAP-97 and, to a lesser extent, PSD-95, is abundantly expressed in human atrial myocardium, while Chapsyn are almost undetectable. Confocal microscopic visualization of cryosection of atrial myocardium stained with the anti-PSD-95 family antibody showed positive staining at the plasma membrane level and cell extremity. Calpain-I cleaved both SAP-97 and PSD-95 proteins, resulting in an accumulation of short bands, including an 80-kDa band that was also detected in the cytosolic protein fraction. Immunoprecipitation of SAP-97 co-precipitated hKv1.5 channels, and vice versa. Co-expression of cloned SAP-97 and hKv1.5 channels in Chinese hamster ovarian (CHO) cells increased the K+ current (157.00±19.45 pA/pF vs. 344.50±58.58 pA/pF at +50 mV). Conclusions: The protein SAP-97 is abundantly expressed in human atrial myocardium in association with hKv1.5 channels, and probably contributes to regulating the functional expression of the latter.
KEYWORDS Arrhythmia; Ion channels; K-channel
* David Godreau and Roger Vranckx contributed equally to this work and should be considered joint first authors.
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