Differential Expression of Gap Junction Proteins in the Canine Sinus Node

Abstract

Abstract-Electrical coupling of pacemaker cells at gap junctions appears to play an important role in sinus node function.Although the major cardiac gap junction protein, connexin43 (Cx43), is expressed abundantly in atrial and ventricular muscle, its expression in the sinus node has been a subject of controversy. The objectives of the present study were to determine whether Cx43 is expressed by sinus node myocytes, to characterize the spectrum of connexin expression phenotypes in sinus node pacemaker cells, and to define the spatial distribution of different connexin phenotypes in the intact sinus node. To fulfill these objectives, we performed high-resolution immunohistochemical analysis of disaggregated adult canine sinus node preparations. Using enhanced tissue preservation and antigen retrieval techniques, we also performed immunohistochemical studies on sections of intact canine sinus node tissue. Analysis of disaggregated sinus node preparations revealed three populations of pacemaker cells distinguished on the basis of connexin immunohistochemical phenotype: Ϸ55% of cells expressed only connexin40 (Cx40); 30% to 35% of cells expressed Cx43, connexin45 (Cx45), and Cx40; and the remaining cells had no detectable connexin expression. In immunostained sections of intact sinus node, Cx43-and Cx45-positive cells were limited in their distribution and were observed in discrete bundles that appeared to abut atrial myocytes. In contrast, Cx40 immunoreactive signal was widely distributed in the sinus node region. These results indicate that subsets of pacemaker cells express distinct connexin phenotypes. Differential expression of connexins could create regions within the sinus node with different conduction properties, thereby contributing to the nonuniform conduction properties seen in this tissue. (Circ Res. 1998;82:604-612.)

Ageing-dependent remodelling of ion channel and Ca2+clock genes underlying sino-atrial node pacemaking

“…This is in agreement with data obtained from the mouse SAN by Verhijck et al (2001) and Miquerol et al (2004). However, Kwong et al (1998) and Coppen et al (1999) reported that Cx40 protein is widely distributed in the SAN of dogs and rabbits, respectively. Therefore, expression of Cx40 in the SAN may vary among species.…”

Cx30.2 can form heteromeric gap junction channels with other cardiac connexins

“…Cx43 was detected using a mouse monoclonal antibody directed against amino acids 252-270 (MAB 3068, Millipore/Chemicon, Billerica, MA) for immunofluorescence or using rabbit polyclonal antibodies directed against amino acids 363-382 of human/rat Cx43 (C6219, SIGMA Chemical Company, St. Louis, MO) for immunoblotting. Cx40 was detected using a mouse monoclonal antibody (39-1700, Invitrogen/Zymed) for immunofluorescence or rabbit antibodies directed against a bacterially expressed fusion protein containing the Cx40 carboxyl tail [17] for immunoblotting. Cx45 was detected using a mouse monoclonal antibody directed against amino acids 354-367 of human Cx45 (MAB 3101, Millipore/Chemicon).…”

Gene Therapy for Cardiac Arrhythmias

“…However, the characteristics of sinus nodal cells also differed in other channels. 27 Thus, the approach to "reprogramming" sinus nodal cells from cardiomyocytes was explored. This novel strategy tried to convert cardiomyocytes into pacemaker cells by introducing a transcription factor.…”