MUSCARINIC DEPOLARIZATION OF SH-SY5Y HUMAN NEUROBLASTOMA-CELLS AS DETERMINED USING OXONOL-V

Membrane potential was measured in the suspension of SH-SY5Y cells usi ng the anionic potentiometric probe, oxonol V. The relation of fluores cence to membrane potential was assessed by increasing the external [K +] in the presence of the K+ ionophore valinomycin. The response was l inear in the range of 5 to 30 mM K+ (membrane potential change of simi lar to 40 mV). Muscarine increased the fluorescence indicating a depol arization. The competitive inhibitory constant (112 nM) of the muscari nic antagonist pirenzepine do[2,3-b](1,4)benzodiazepin-6-one-dihydroch loride) suggests that Hm1 receptors are not involved. The protein kina se C inhibitor, GF 109203X minopropyl)-indol-3-yl]-3-(indol-3-yl)-male imide), and a reduction of extracellular Na+ both produced an additive partial inhibition. The results suggest that muscarinic receptors dep olarize these cells by separate Na+-dependent and -independent mechani sms, the Na+-independent mechanism being protein kinase C-dependent.