Effects of hypo-osmotic stress on ATP release in isolated turbot (Scophthalmus maximus) hepatocytes.
BACKGROUND
ATP is released from many cell types exposed to hypo-osmotic shock and is involved in RVD (regulatory volume decrease). Purinergic signalling events have been extensively investigated in mammals, but not in marine teleosteans.


RESULTS
The effect of hypo-osmotic shock on ATP release was examined in isolated hepatocytes from turbot (Scophthalmus maximus), a marine flatfish. Hypo-osmotic stress (240 mOsm x kg(-1)) induced a significant increase in ATP efflux, and was inhibited by a potential CFTR (cystic fibrosis transmembrane conductance regulator) inhibitor, glibenclamide, but not by the MDR1 (multidrug resistance 1) P-glycoprotein inhibitor, verapamil. ATP efflux could be a cAMP-dependent process, as IBMX (isobutylmethylxanthine) and forskolin triggered the process under iso-osmotic conditions. Protein kinases, including protein kinase C, could also be involved, as staurosporine and chelerythrine inhibited the mechanism. Calcium could contribute to ATP efflux as ionomycin, a calcium ionophore, elicited a rapid release under iso-osmotic conditions, and chelation using EGTA abolished ATP release under hypo-osmotic conditions. RVD was partially abolished by apyrase, an ATP scavenger, and suramin, a purinoceptor antagonist. Moreover, hypo-osmotic shock induced a rise in intracellular calcium which could be involved in RVD. Since extracellular ATP triggered an increase in cellular free-calcium content under iso-osmotic conditions, our results could indicate that hypo-osmotic-induced ATP efflux contributes to RVD in turbot hepatocytes by stimulating purinergic receptors, which may lead to activation of a calcium signalling pathway.


CONCLUSIONS
These data provide the first evidence of volume-sensitive ATP signalling for volume maintenance in a marine teleost fish cell type.
Ollivier
Hélène
H
Unité de Physiologie Comparée et Intégrative, U.F.R. Sciences et Techniques, 6 Avenue Le Gorgeu CS 93837, 29238 Brest, Cedex 3, France. Helene.Ollivier@univ-brest.fr
Pichavant-Rafini
Karine
K
Puill-Stephan
Eneour
E
Calvès
Patrick
P
Nonnotte
Liliane
L
Nonnotte
Guy
G
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002469:Cell Separation; D048429:Cell Size; D005412:Flatfishes / Q000502:physiology*; D022781:Hepatocytes / Q000502:physiology*; D008163:Luminescent Measurements; D009997:Osmotic Pressure; D011983:Receptors, Purinergic / Q000378:metabolism; D015398:Signal Transduction
D011983:Receptors, Purinergic; D000255:Adenosine Triphosphate