Aminoguanidine has potential pharmacologic utility for diabetes and nitric oxide - mediated inflammation. Because aminoguanidine is positively charged at physiologic pH (pK(a) similar to 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 mu M, n = 3, versus high passage, 101.7 +/- 5.6 mu M, 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*mu M), n = 3, high passage, 1.1 +/- 0.2 pmol/(min*mg proteins*mu M) 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. (C) 2000 Elsevier Science B.V. All rights reserved.
