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Departments of Medical Education and Research (S.-N.W.) and Internal Medicine (H.-T.C.) and Section of Neurology (Y.-K.L.), Kaohsiung Veterans General Hospital, Kaohsiung City, Taiwan; Institute of Biomedical Sciences, National Sun Yat-Sen University (S.-N.W.), Kaohsiung City, Taiwan; and National Yang-Ming University (Y.-K.L., I.-T.K., H.-T.C.), Taipei City, Taiwan
Address all correspondence and requests for reprints to: Sheng-Nan Wu, M.D., Ph.D., Department of Medical Education and Research, Kaohsiung Veterans General Hospital, No. 386, Ta-Chung First Road, Kaohsiung City, Taiwan, Republic of China. E-mail: snwu{at}isca.vghks.gov.tw
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). TNF
(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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