Agmatine and putrescine uptake in the human glioma cell line SK-MG-1

The pharmacological properties of a specific agmatine uptake mechanism were investigated in the human glioma cell line SK-MG-1 and compared with those of the putrescine transporter expressed by the same cells and with those o f several other organic cation transport systems or ion channels reported i n the literature. The specific accumulation of [C-14]agmatine at 37 degreesC above nonspecifi c accumulation at 4 degreesC was energy-dependent and saturable with a V-ma x of 64.3+/-3.5 nmol/min per mg protein and a K-m of 8.6+/-1.4 muM. Specifi c accumulation was attenuated by replacement of extracellular Na+ by cholin e by 65%, not affected by lithium and enhanced by replacement by sucrose. P hentolamine, clonidine, 1,3-di-(2-tolyl)guanidine, histamine, putrescine, s permine and spermidine were inhibitors of specific [C-14]agmatine accumulat ion. In contrast, corticosterone, desipramine, O-methylisoprenaline, cirazo line, moxonidine, L-arginine, L-lysine, verapamil, nifedipine and CdCl2 at concentrations up to 10 mM failed to inhibit specific [14C]agmatine accumul ation, thus excluding that the latter is mediated by amino acid or monoamin e carriers, by Ca2+ channels or by the organic cation transporters OCT1, OC T2, OCT3, OCTN1 or OCTN2. The pattern of activity of inhibitory compounds w as also different from that determined for specific putrescine accumulation found in the same cells (K-m 1.3+/- 0.1 muM, V-max 26.1+/-0.4 nmol/min per mg protein) ruling out an identity of the specific [C-14]agmatine and [C-1 4]putrescine accumulation mechanisms. It is concluded that specific accumulation of agmatine in human glioma cell s is mediated by a specific transporter whose pharmacological properties ar e not identical to those of the agmatine transporter previously identified in rat brain synaptosomes and to other so far known carrier mechanisms for organic cations and ion channels. The agmatine uptake system may be importa nt for the regulation of the extracellular concentration of agmatine in man .