Nitric oxide enhances de novo formation of endothelial gap junctions.
OBJECTIVE
Gap junctions (formed by connexins, Cx) are important for functional coordination of cells in the vascular wall. However, little is known about their physiological regulation in this tissue. We examined the effects of nitric oxide (NO), an important mediator of vasomotion, wound healing and angiogenesis, on the formation of gap junctions in endothelial cells (human umbilical vein endothelial cells, HUVEC).


METHODS
Flow cytometry was used to determine dye transfer through newly formed gap junctions between acutely coincubated HUVECs. Parallel experiments in wild-type HeLa cells (no connexins) and transfected HeLa cells exclusively expressing Cx43, Cx40 or Cx37 were performed to determine the specific role of Cx subtypes. The intracellular distribution of Cx40 was examined after fractionation with triton by Western blotting. Intracellular levels of cGMP and cAMP were measured by radioimmunoassay.


RESULTS
The NO donor SNAP (1 microM) enhanced gap-junctional coupling in HUVECs by about 40%. This was associated with an enhanced incorporation of Cx40 into the membrane. Both effects were restricted to Cx40 as analyzed in experiments with Cx-selective HeLa cells. The NO-induced increase in cell coupling was elicited by a corresponding rise of cGMP, which secondarily increased intracellular cAMP levels. The latter was an integral part of the signal cascade, since the protein kinase A (PKA) inhibitor H89 blocked the SNAP-induced incorporation of Cx40 into the plasma membrane.


CONCLUSIONS
We conclude that NO is a potent modulator of gap-junctional coupling in endothelial cells. It enhances de novo formation of endothelial gap junctions by increasing incorporation of Cx40 into the plasma membrane due to PKA activation.
Hoffmann
Anke
A
Institute of Physiology, Ludwig-Maximilians-University Munich, Schillerstrasse 44, 80336 Munich, Germany.
Gloe
Torsten
T
Pohl
Ulrich
U
Zahler
Stefan
S
D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D004396:Coloring Agents; D017630:Connexins / Q000235:genetics / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D004789:Enzyme Activation; D005434:Flow Cytometry; D017629:Gap Junctions / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D009569:Nitric Oxide / Q000494:pharmacology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D013449:Sulfonamides; D014665:Vasodilator Agents / Q000494:pharmacology*; D000097003:Gap Junction alpha-5 Protein
D004396:Coloring Agents; D017630:Connexins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D006152:Cyclic GMP; D007546:Isoquinolines; D009569:Nitric Oxide; D020030:Nitric Oxide Donors; D010396:Penicillamine; D013449:Sulfonamides; D014665:Vasodilator Agents; D000097003:Gap Junction alpha-5 Protein; C110881:S-nitro-N-acetylpenicillamine; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide