Stimulation of norepinephrine transporter function by fasudil, a Rho kinase inhibitor, in cultured bovine adrenal medullary cells

Norepinephrine transporter (NET) regulates noradrenergic synaptic transmission by controlling extracellular levels of norepinephrine (NE). The small GTPase, RhoA, and its downstream effector Rho kinase (ROCK) are involved in the regulation of actin cytoskeleton and focal adhesion/stress fiber formation, which may play an important role in various functions of the sympathetic nervous system. We report here the effect of fasudil, a ROCK inhibitor, on the functions of NET in cultured bovine adrenal medullary cells as a model of sympathetic neurons. Treatment of bovine adrenal medullary cells with fasudil caused an increase in [3H]NE uptake in time (8–120 h) and concentration (10–100 μM)-dependent manner. Another ROCK inhibitor, Y-27632 (10–100 μM, 1 day), also increased [3H]NE uptake by the cells. Kinetics analysis of the effect of fasudil on NE transport showed a significant increase in the Vmax of NE transport with little change in Km. When both extracellular and intracellular Ca2+ were removed by the deprivation of extracellular Ca2+ and BAPTA-AM, a cell-permeable Ca2+ chelator, [3H]NE uptake induced by fasudil was completely abolished. Nocodazole, an inhibitor of microtubule polymerization, but not cytochalasin D, an inhibitor of actin polymerization, suppressed the stimulatory effect of fasudil on [3H]NE uptake. The present findings suggest that the ROCK inhibitor fasudil up-regulates NET function in a Ca2+-dependent and/or nocodazole-sensitive pathway in adrenal medullary cells.