Ceramide inhibits the inwardly rectifying potassium current in GH(3) lactotrophs

The effects of ceramide on ion currents in rat pituitary GH(3) cells were i nvestigated. Hyperpolarization-elicited K+ currents present in GH(3) cells were studied to determine the effect of ceramide and other related compound s on the inwardly rectifying K+ current (I-K(IR)). Ceramide (C-2-ceramide) suppressed the amplitude of I-K(IR) in a concentration-dependent manner, wi th an IC50 value of 5 muM. Ceramide caused a rightward shift in the midpoin t for the activation curve of I-K(IR). Pretreatment with PD-98059 (30 muM) or U-0126 (30 mum) did not prevent ceramide-mediated inhibition of IK(IR,. However, the magnitude of ceramide-induced inhibition of IR(m) was attenuat ed in GH(3)cells preincubated with dithiothreitol (10 mum). TNF alpha (100 ng/g) also suppressed I-K(IR). In the inside-out configuration, application of ceramide (30 mum) to the bath slightly suppressed the activity of large conductance Ca2+-activated K+ channels. Under the current clamp mode, cera mide (10 muM) increased the firing of action potentials. Cells that exhibit ed an irregular firing pattern were converted to those displaying a regular firing pattern after application of ceramide (10 muM). Ceramide also suppr essed I-K(IR) in neuroblastoma IMR-32 cells. Therefore, ceramide can produc e a depressant effect on I-K(IR). The blockade of this current by ceramide may affect cell function.