Synergism between hypotonically induced calcium release and fatty acyl-CoA esters induced calcium release from intracellular stores.
The non-mitochondrial Ca2+ stores in permeabilized A7r5 cells responded to a decrease in Mg-ATP concentration with a pronounced Ca2+ release if 20 microM CoA was present. This release was rather specific for the preincubation or removal of ATP. ATP gamma S was much less effective and AMP-PNP, GTP, ITP, CTP, UTP, ADP, AMP, adenosine and adenine had no effect. CoA activated with an EC50 of 6 microM. Dephospho-CoA was a less effective cofactor and desulfo-CoA was ineffective. The release induced by Mg-ATP removal did not occur in the presence of 2% fatty acid-free bovine serum albumin and did not develop at 4 degrees C. All these findings suggest that CoA had to be acylated by endogenous fatty-acyl-CoA synthetase to become effective. Myristoyl- and palmitoyl-CoA esters were identified as the most effective cofactors for the release. Ca2+ release induced by removing Mg-ATP did not occur if the osmolality of the medium was kept constant by addition of mannitol, sucrose, KCl, MgCl2 or Mg-GTP, indicating that the decrease in tonicity was the trigger for the release. Mg-ATP plus CoA also synergized with Ca2+ release induced by a hypotonic shock imposed by diluting the medium with H2O. Osmolality changes induced by decreasing the Mg-ATP concentration were more effective in releasing Ca2+ than equal decreases in concentration of all solutes. We conclude that fatty acyl-CoA esters sensitize the hypotonically induced Ca2+ release from the non-mitochondrial Ca2+ stores.
Missiaen
L
L
Laboratorium voor Fysiologie, KU Leuven Campus Gasthuisberg, Belgium. Ludwig.Missiaen@med.kuleuven.ac.be
De Smedt
H
H
Parys
J B
JB
Sipma
H
H
Maes
K
K
Vanlingen
S
S
Sienaert
I
I
Van Driessche
W
W
Casteels
R
R
D000214:Acyl Coenzyme A / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D007038:Hypotonic Solutions; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009994:Osmolar Concentration; D010171:Palmitoyl Coenzyme A / Q000378:metabolism*; D051381:Rats
D000214:Acyl Coenzyme A; D007038:Hypotonic Solutions; D010171:Palmitoyl Coenzyme A; C040349:S-tetradecanoyl-coenzyme A; D000255:Adenosine Triphosphate; D002118:Calcium