Decrease in acetylcholine-induced current by neomycin in PC12 cells

The effects of neomycin, one of the aminoglycoside antibiotics, on the acetylcholine (ACh)-induced current (IACh) were studied in pheochromocytoma cells by using the whole-cell clamp technique. The IACh proved to be generated through neuronal nicotinic receptor. ACh (30 μM) induced an inward current at a holding potential of −80 mV. When cells were treated with neomycin (0.01–1 mM) and ACh (30 μM) simultaneously, an inhibitory effect of neomycin on the peak of IACh was found. This effect was fast, reversible, and concentration dependent. Pretreatment with neomycin for 3–8 min had no effect on the inhibition of IACh induced by neomycin. External application of 0.1 mM neomycin neither shifted the dose–response curve of the peak IACh to the right (dissociation constant (Kd) = 16.5 μM) nor affected its coefficient (1.8) but inhibited the curve amplitudes by ∼33%. Stimulated protein kinase C activation by using an exogenous activator produced inhibition of IACh, while using protein kinase C inhibitor (PKCI 19-31) had no effect on the inhibition of IACh induced by neomycin. These results suggest that neomycin has an inhibitory effect on IACh without the involvement of phospholipase C. It indicates that neomycin binds to a specific site on the cell membrane, probably on the neuronal nicotinic receptor-coupled channel, and inhibits the IACh in a noncompetitive manner, thus controlling the immediate catecholamine release from the sympathetic cells.