Carnitine uptake into human heart cells in culture

The uptake of radiolabeled carnitine and butyrobetaine has been studied in human heart cells (CCL 27). The uptake of carinitine is 3-10-fold higher in heart cells than in fibroblasts (pmol - mug DNA-1). The uptake of carnitine increases with temperature coefficient KT of 1.6 in the interval 10-20 degrees C and with a negligible uptake at 4 and 10 degrees C. The uptake of carnitine follows Michaelis-Menten kinetics with a KM of 4.8 +/- 2.2 muM and V = 8.7 +/- 3.2 pmol - mug DNA-1 - H-1. Carnitine uptake is suppressed 90% by NaF (24MM). Butyrobetaine is taken up into heart cells to the same extent as carnitine with a KM of 5.7-17.3 muM and V = 8.7-9.3 pmol - mug DNA-1 - h-1. Butyrobetaine inhibits competitively the uptake of carnitine and carnitine inhibits the uptake of butyrobetaine to the same extent. No conversion of radiolabeled butyrobetaine to carnitine, or carnitine to methyl choline was observed intra- or extracellulary during incubation. These data are compatible with a selective transport mechanism for carnitine which is also responsible for the uptake of butyrobetaine.