Accumulation of 1‐Methyl‐4‐Phenyl‐1,2,3,6‐Tetrahydropyridine in Cultured Cerebellar Astrocytes

Abstract: Cultured cerebellar astrocytes rapidly accumulate 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) from the incubation medium, reaching a plateau within 10 min, whereas within that time negligible amounts of 1‐methyl‐4‐phenylpyridinium (MPP⁺) have entered the astrocytes. MPTP accumulation is essentially independent of temperature and is proportional to extracellular concentration at steady state: The steady‐state concentration achieved within these cells is about 50‐fold higher at relatively low extracellular concentrations. MPTP appears to accumulate intracellularly within lysosomes, because lysosomotropic agents such as ammonium chloride and chloroquine markedly diminish the accumulation. Moreover, a proton gradient is required, because MPTP accumulation is abolished by the hydrogen ion antiporter monensin. Over an interval of several days, MPTP is converted to MPP⁺ intracellularly, with a concomitant decrease in medium MPTP and increase in medium MPP⁺. A constant, small but significant amount of MPP⁺ is retained intracellularly over a 72‐h interval. Increasing the medium MPTP concentrations results in increased conversion of MPTP and enhanced intracellular retention of MPTP and MPP⁺. Neither MPTP nor MPP⁺ is neurotoxic to cultured cerebellar astrocytes as determined by cell counts and rate of conversion of MPTP to MPP⁺.