Myocardial interstitial choline and glutamate levels during acute myocardial ischaemia and local ouabain administration.
OBJECTIVE
Noradrenaline (NA) uptake transporters are known to reverse their action during acute myocardial ischaemia and to contribute to ischaemia-induced myocardial interstitial NA release. By contrast, functional roles of choline and glutamate transporters during acute myocardial ischaemia remain to be investigated. Because both transporters are driven by the normal Na+ gradient across the plasma membrane in a similar manner to NA transporters, the loss of Na+ gradient would affect the transporter function, which would in turn alter myocardial interstitial choline and glutamate levels. The aim of the present study was to examine the effects of acute myocardial ischaemia and the inhibition of Na+,K+-ATPase on myocardial interstitial glutamate and choline levels.


METHODS
In anaesthetized cats, we measured myocardial interstitial glutamate and choline levels while inducing acute myocardial ischaemia or inhibiting Na+,K+-ATPase by local administration of ouabain.


RESULTS
The choline level was not changed significantly by ischaemia (from 0.93 +/- 0.06 to 0.82 +/- 0.13 microm, mean +/- SE, n = 6) and was decreased slightly by ouabain (from 1.30 +/- 0.06 to 1.05 +/- 0.07 microm, P < 0.05, n = 6). The glutamate level was significantly increased from 9.5 +/- 1.9 to 34.7 +/- 6.1 microm by ischaemia (P < 0.01, n = 6) and from 8.9 +/- 1.0 to 15.9 +/- 2.3 microm by ouabain (P < 0.05, n = 6). Inhibition of glutamate transport by trans-L-pyrrolidine-2,4-dicarboxylate (t-PDC) suppressed ischaemia- and ouabain-induced glutamate release.


CONCLUSIONS
Myocardial interstitial choline level was not increased by acute myocardial ischaemia or by Na+,K+-ATPase inhibition. By contrast, myocardial interstitial glutamate level was increased by both interventions. The glutamate transporter contributed to glutamate release via retrograde transport.
Kawada
T
T
Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan. torukawa@res.ncvc.go.jp
Yamazaki
T
T
Akiyama
T
T
Shishido
T
T
Mori
H
H
Sugimachi
M
M
D000109:Acetylcholine / Q000032:analysis; D000208:Acute Disease; D000818:Animals; D002415:Cats; D002794:Choline / Q000032:analysis*; D003331:Coronary Vessels / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018698:Glutamic Acid / Q000032:analysis*; D006321:Heart / Q000187:drug effects; D017202:Myocardial Ischemia / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
D004791:Enzyme Inhibitors; D018698:Glutamic Acid; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D002794:Choline; D000109:Acetylcholine