Functional differences between human Cx37 polymorphic hemichannels.
A polymorphism in the human Cx37 gene (C1019T), resulting in a non-conservative amino acid change in the regulatory C-terminus of the Cx37 protein (P319S), has been proposed as a prognostic marker for atherosclerosis. We have recently demonstrated that Cx37 hemichannels control the initiation of atherosclerotic plaque development by regulating ATP-dependent monocyte adhesion in atherosclerosis-susceptible apolipoprotein E-deficient mice. In this study, we have measured the electrical properties of Cx37 hemichannels (HCs) and gap junction channels (GJCs) with voltage-clamp methods. To this end, we have transfected hCx37-P319, hCx37-S319 or empty pIRES-eGFP vector cDNA into communication-deficient HeLa cells. In clones expressing similar levels of Cx37, exposure of single cells to low-Ca(2+) solution induced a voltage-sensitive HC current. The analysis yielded a bell-shaped function g(hc)=f(V(m)) (g(hc): normalized conductance at steady state; V(m): membrane potential) with a maximum around V(m)=-30 mV. The peak g(hc) of Cx37-P319 was 3-fold larger than that of Cx37-S319 HCs. Experiments on cell pairs revealed that Cx37-P319 GJCs exhibited a 1.5-fold larger unitary conductance than Cx37-S319 GJCs. Hence, the larger peak g(hc) of the former may reflect a larger conductance of their HCs. Using the same clones, we found that Cx37-P319 cells released more ATP and were less adhesive than Cx37-S319 cells. The reduction in adhesiveness of Cx37-expressing cells was prevented by extracellular apyrase. We conclude that the differences in biophysical properties between polymorphic HCs may be responsible for inequality in ATP release between Cx37-P319 and Cx37-S319 cells, which results in differential cell adhesion.
Derouette
Jean-Paul
JP
Department of Internal Medicine, Division of Cardiology, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
Desplantez
Thomas
T
Wong
Cindy W
CW
Roth
Isabelle
I
Kwak
Brenda R
BR
Weingart
Robert
R
D000255:Adenosine Triphosphate / Q000378:metabolism; D002448:Cell Adhesion; D017630:Connexins / Q000235:genetics* / Q000378:metabolism*; D055724:Electrophysiological Phenomena; D017629:Gap Junctions / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D011110:Polymorphism, Genetic; D014162:Transfection; D000097006:Gap Junction alpha-4 Protein
D000255:Adenosine Triphosphate; D017630:Connexins; D000097006:Gap Junction alpha-4 Protein