Pd. Prasad et al., SODIUM-DEPENDENT CARNITINE TRANSPORT IN HUMAN PLACENTAL CHORIOCARCINOMA CELLS, Biochimica et biophysica acta. Biomembranes, 1284(1), 1996, pp. 109-117
The JAR human placental choriocarcinoma cells were found to transport
carnitine into the intracellular space by a Na+-dependent process. The
transport showed no requirement for anions. The Na+-dependent process
was saturable and the apparent Michaelis-Menten constant for carnitin
e was 12.3 +/- 0.5 mu M. Na+ activated the transport by increasing the
affinity of the transport system for carnitine. The transport system
specifically interacted with L-carnitine, D-carnitine, acetyl-DL-carni
tine and betaine. 6-N-Trimethyllysine and choline had little or no eff
ect on carnitine transport. Of the total transport measured, transport
into the intracellular space represented 90%. Plasma membrane vesicle
s prepared from JAR cells were found to bind carnitine in a Na+-depend
ent manner. The binding was saturable with an apparent dissociation co
nstant of 0.66 +/- 0.08 mu M. The binding process was specific for L-c
arnitine, D-carnitine, acetyl-DL-carnitine, and betaine. 6-N-Trimethyl
lysine and choline showed little or no affinity. It is concluded that
the JAR cells express a Na+-dependent high-affinity system for carniti
ne transport and that the Na+-dependent high-affinity carnitine bindin
g detected in purified JAR cell plasma membrane vesicles is possibly r
elated to the transmembrane transport process.