Cellular transport processes of aminoguanidine, a nitric oxide synthase inhibitor, in the opossum kidney cell culture line

Aminoguanidine has potential pharmacologic utility for diabetes and nitric oxide - mediated inflammation. Because aminoguanidine is positively charged at physiologic pH (pK(a)˜10), it is unlikely that simple diffusion is a predominant mechanism for cellular penetration. This study sought to determine the transport processes by which aminoguanidine, a cationic compound, traverses across cellular membranes. In cultured opossum kidney (OK) cell monolayers, aminoguanidine transport involved both saturable and non-saturable diffusion processes. At passage numbers below 67, the observed V(max) and K(m) for saturable influx were significantly lower than that observed at passages greater than 79 (V(max): low passage, 21.2 ± 7.8 pmol/(min*mg protein), n=3; versus high passage, 129.7 ± 24.3 pmol/(min*mg protein), n=3, P < 0.05; K(m): low passage, 23.7 ± 10.8 μM, n=3; versus high passage, 101.7 ± 5.6 μM, n=3, P < 0.05; mean ± S.E.M.). Nonsaturable processes were not statistically different (k(ns): low passage, 1.6 ± 0.1 pmol/(min*mg protein*μM), n=3; high passage, 1.1 ± 0.2 pmol/(min*mg protein*μM) n=3). Saturable influx was temperature dependent, and independent of ATP energy, sodium gradients or changes in membrane potential. Other organic cations competitively inhibited and trans-stimulated saturable influx. Aminoguanidine influx was increased in the presence of an outwardly- directed proton gradient and was inhibited in the presence of an inwardly- directed proton gradient. Correspondingly, aminoguanidine efflux was trans- stimulated by aminoguanidine and guanidine. In summary, OK cell cultures at high passage numbers (>79) express a saturable, bi-directional carrier- mediated process to transport aminoguanidine across cellular membranes.