UPTAKE AND RELEASE OF CARNITINE BY VASCULAR ENDOTHELIUM IN CULTURE - EFFECTS OF PROTONS AND OXYGEN-FREE RADICALS

The present paper shows that cultured bovine endothelial cells can be labeled with H-3-carnitine by incubation. This process is slow and is uphill, requiring Na+/K(+)ATPase activity. After 3 days incubation iso topic equilibrium is reached, when the cells contain about 0.5 mM (tot al) carnitine at a medium concentration of about 3 mu M. The plasmamem brane barrier is rather resistant to acidosis and oxygen free radicals (OFR). The rate of carnitine release increases significantly only at pH below 5.8. At pH 6.0 the release of stored carnitine can be initiat ed by the addition of D- or L-lactate. OFR, generated by the addition of xanthine and xanthine oxidase, did not affect carnitine release. Bo th mild acidosis and OFR left plasmamembranes of endothelial cells int act as judged by the absence of lactate dehydrogenase loss from the ce lls, Therefore, the known increase of capillary permeability during is chemia and reperfusion may not be due to plasmalemmal disruption of in dividual endothelial cells, but to increase of inter-endothelial space s.