Relationship Between Connexin Expression and Gap–Junction Resistivity in Human Atrial Myocardium

Abstract

Background-The relative roles of the gap-junctional proteins connexin40 (Cx40) and connexin43 (Cx43) in determining human atrial myocardial resistivity is unknown. In addressing the hypothesis that changing relative expression of Cx40 and Cx43 underlies an increase in human atrial myocardial resistivity with age, this relationship was investigated by direct ex vivo measurement of gap-junctional resistivity and quantitative connexin immunoblotting and immunohistochemistry. Methods and Results-Oil-gap impedance measurements were performed to determine resistivity of the intracellular pathway (R i ), which correlated with total Cx40 quantification by Western blotting (r s =0.64, P<0.01, n=20). Specific gapjunctional resistivity (R j ) correlated not only with Western immunoquantification of Cx40 (r s =0.63, P=0.01, n=20), but also more specifically, with the Cx40 fraction localized to the intercalated disks on immunohistochemical quantification (r s =0.66, P=0.02, n=12). Although Cx43 expression showed no correlation with resistivity values, the proportional expression of the 2 connexins, (Cx40/[Cx40+Cx43]) correlated with R i and R j (r s =0.58, P<0.01 for R i and r s =0.51, P=0.02 for R j ). Advancing age was associated with a rise in R i (r s =0.77, P<0.0001), R j (r s =0.65, P<0.001, n=23), Cx40 quantity (r s =0.54, P=0.01, n=20), and Cx40 gap-junction protein per unit area of en face disk (r s =0.61, P=0.02, n=12). Conclusions-Cx40 is associated with human right atrial gap-junctional resistivity such that increased total, gap-junctional, and proportional Cx40 expression increases gap-junctional resistivity. Accordingly, advancing age is associated with an increase in Cx40 expression and a corresponding increase in gap-junctional resistivity. These findings are the first to demonstrate this relationship and a mechanistic explanation for changing atrial conduction and age-related arrhythmic tendency. Patients and Methods Specimen Source, Collection, and HandlingThe use of human tissue conformed to the principles outlined in the Declaration of Helsinki, and the study had local Ethical Committee approval with written informed consent. Atrial appendage biopsies were collected from patients undergoing cardiac surgery at The London Chest Hospital, London, UK. Twenty-three patients (15 male) in sinus rhythm (age 68±8 years, range 53-80 years) undergoing coronary bypass surgery (n=15), aortic valve replacement (n=3), or both (n=5) were included. Patients were in sinus rhythm at the time of surgery as assessed by ECG and did not have any history of atrial arrhythmia. All patients underwent surgery using conventional cardiopulmonary bypass support, and biopsies were collected from the tips of the right atrial appendage immediately after the pericardium was opened and before exposure to cardioplegic agents. Samples were divided immediately on collection; one part was snap-frozen in liquid nitrogen at −70ºC for subsequent Cx quantification and immunolabeling, and the remainder was transported to the laboratory in preoxyge...

The Rotor Revolution

“…First, naturally occurring variations in connexin expression correlate with conduction velocity (CV) with a direct relationship linking GJ resistivity and CV in humans 28 and animals 19a,29 ( Figure 4). Second, studies in human myocardium indicate a direct role for GJ remodeling in the electrophysiological changes in heart failure.…”

Connexin40 abnormalities and atrial fibrillation in the human heart

“…Thus, our AF heart samples might contain areas with faster as well as slower local conduction and might vary substantially. In human atrium, the relative abundance of Cx40 as detected by immunolocalization or by immunoblotting has been correlated with reduced conduction velocity [9] and with the increased atrial resistivity associated with aging [23]. …”

Regulation of gap junction conductance by calcineurin through Cx43 phosphorylation: implications for action potential conduction

“…G j was measured with preparations in an oil-gap chamber and calculated from the frequency-dependent (0.02–300 kHz) total longitudinal impedance, z i —the method and its validation have been detailed elsewhere [3, 8]. After control readings in Tyrode’s solution, preparations were exposed to low-Na solution to raise the intracellular [Ca 2+ ], with or without Cn or PP1/PP2A inhibitors, for 20–30 min before new readings were taken.…”

“…In all preparations, CV was measured with a stimulus voltage 1.5 times the threshold value. Values of the maximum rate of depolarisation during the AP upstroke (d V /d t max ) and the time constant of the AP subthreshold region (AF foot, τ ap , [8]) were also recorded.…”