The effects of ceramide on ion currents in rat pituitary GH3 cells were investigated. Hyperpolarization-elicited K+ currents present in GH3 cells were studied to determine the effect of ceramide and other related compounds on the inwardly rectifying K+ current (IK(IR)). Ceramide (C2-ceramide) suppressed the amplitude of IK(IR) in a concentration-dependent manner, with an IC50 value of 5 μM. Ceramide caused a rightward shift in the midpoint for the activation curve of IK(IR). Pretreatment with PD-98059 (30 μM) or U-0126 (30 μM) did not prevent ceramide-mediated inhibition of IK(IR). However, the magnitude of ceramide-induced inhibition of IK(IR) was attenuated in GH3 cells preincubated with dithiothreitol (10 μM). TNFα (100 ng/g) also suppressed IK(IR). In the inside-out configuration, application of ceramide (30 μM) to the bath slightly suppressed the activity of large conductance Ca2+-activated K+ channels. Under the current clamp mode, ceramide (10 μM) increased the firing of action potentials. Cells that exhibited an irregular firing pattern were converted to those displaying a regular firing pattern after application of ceramide (10 μM). Ceramide also suppressed IK(IR) in neuroblastoma IMR-32 cells. Therefore, ceramide can produce a depressant effect on IK(IR). The blockade of this current by ceramide may affect cell function.
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