INTERINDIVIDUAL VARIATION IN TOTAL AND CARRIER-MEDIATED LACTATE INFLUX INTO RED-BLOOD-CELLS

To study in standardbred horses interindividual variation in the influ x of lactate into red blood cells, venous blood samples were collected from 89 horses from 2 wk to 9 yr of age. For 62 horses, the rate of i nflux was normally distributed with a mean rate of 4.09 nmol.mg protei n(-1).min(-1) at a lactate concentration of 10 mM, and the respective value for the other 27 horses was 0.58 nmol.mg protein(-1).min(-1). At 30 mM of lactate, the rates were 8.71 and 1.97 nmol.mg protein(-1).mi n(-1), respectively. This bimodal distribution was independent of age. In horses with high transport activity, the monocarboxylate transport er (MCT) appears to be the major carrier, whereas, in those with low t ransport activity, no activity of the MCT could be detected. The band 3 protein may account for 18-39% of transport activity. With all age g roups combined, the transport activity tended to be higher in mares th an in stallions. Lactate transport into red blood cells seems thus to be an inherent property in which participation of various transporters varies interindividually.