ATP Release Via Connexin Hemichannels Controls Intercellular Propagation of Ca Waves in Corneal Endothelial Cells - Extracellular ATP and Adenosine as Regulators of Endothelial Cell Function - page 156

Chapter 10
ATP Release Via Connexin Hemichannels
Controls Intercellular Propagation of Ca 2+
Waves in Corneal Endothelial Cells

Raf Ponsaerts, Catheleyne D'hondt, Priya Gomes, Geert Bultynck,
Sangly P. Srinivas, Johan Vereecke, and Bernard Himpens

Abstract Intercellular communication (IC) is essential for coordinating cellular
activity in multi-cellular organisms, and plays a role in many physiological and
pathological processes. Direct IC between adjacent cells is mainly mediated by gap
junctions, whereas paracrine signaling provides an indirect pathway for IC between
neighboring cells. Purinergic mediators are important messengers in this paracrine
signaling, and recent evidence shows that connexin and pannexin hemichannels
form an important release pathway for ATP involved in purinergic IC.
We have investigated the properties of IC via Ca 2+ waves evoked by mechani-
cal stimulation of a single cell in monolayers of bovine corneal endothelial cells
(BCEC). We have demonstrated that both gap junctions and paracrine IC are
involved in the Ca 2+ wave propagation, and that purinergic paracrine signaling is
the main component of IC in BCEC. Furthermore, our results demonstrate that con-
nexin43 hemichannels provide the pathway for ATP release. Our experiments show
that the paracrine IC is strongly reduced in the presence of inflammatory agents,
such as histamine and thrombin, that enhance actomyosin contraction. The effect of
these agents is due to inhibition of hemichannel-mediated ATP release. This effect
of thrombin can be precluded by preincubation of the cells with adenosine. Possible
roles of paracrine IC to “bystander” and “good Samaritan” effects are discussed.

Keywords Intercellular communication · Cornea · Endothelial cells · Calcium

wave · Mechanical stimulation · Connexin · Gap junction · Paracrine

signaling · Hemichannels · Purinergic · ATP release · Thrombin ·

Histamine · Adenosine · Rho kinase · Phosphorylation · Myosin light chain · Myosin

ATPase activity · Contractility · Cytoskeleton · Blebbistatin · Bystander

effect · Good Samaritan effect

B

J. Vereecke ( )

Laboratory of Molecular and Cellular Signaling, Department of Molecular Cell Biology,
KULeuven, Campus Gasthuisberg O&N1, B-3000 Leuven, Belgium
e-mail: [e-mail]