TRANSPORT OF 3-HYDROXYBUTYRATE BY CULTURED RAT-BRAIN ASTROCYTES

It is well established that 3-hydroxybutyrate can serve as an energy s ource for the brain. Since substrate utilization may be regulated in p art by transport across the cellular membrane, we investigated the upt ake of 3-hydroxybutyrate by primary cultures of rat brain astrocytes. Measurement of the net uptake indicated a saturable system and a Linew eaver-Burke type plot was consistent with a single carrier-mediated me chanism with a Km of 6.03 mM and a Vmax of 32.7 nmol/30 seconds/mg pro tein. The rate of uptake at pH 6.2 was more than ten times the rate at pH 8.2 with the rate at pH 7.4 being intermediate between these value s, suggesting the possibility of. cotransport with H+ or exchange with OH- (antiport). Mersalyl had only a slight effect on the transport of 3-hydroxybutyrate, suggesting that sulfhydryl groups are not involved in the transport of this monocarboxylic acid. Phenylpyruvate and alph a-ketoisocaproate also attenuated the transport, but lactate had only a marginal effect. These results suggest that the utilization of 3-hyd roxybutyrate as an energy source by astrocytes is regulated in part by carrier-mediated transport and that the uptake system is different fr om the lactate transport system.