Ceramide inhibits the outward potassium current in rat pinealocytes.
In the present study, we investigated the effect of ceramide on the outward K(+) current in rat pinealocytes using whole cell and single channel recordings. Three components of the whole cell outward K(+) current were separated, an iberiotoxin (IBTX)-sensitive K(+) current (I(KCa)), a transient A current (I(A)) and a delayed rectifier current (I(K)). C6-ceramide reduced all three components of the outward K(+) current. C6-ceramide (30 microM) caused a 53% inhibition of I(KCa) [a component that is generated by the IBTX-sensitive K(+) channel (BK channel)], a 27% inhibition of I(A) and a 17% inhibition of I(K). Additional studies showed that the BK channel was not inhibited by dihydroC6-ceramide, the inactive analog of C6-ceramide, but mimicked by sphingomyelinase which increased intracellular ceramide. The ceramide inhibition of the BK channel was only partly dependent on its inhibition of the L-type Ca(2+) channel. Studies using specific kinase inhibitors showed that calphostin C (a protein kinase C inhibitor) and to a lesser degree lavendustin A (a tyrosine kinase inhibitor) were effective in reducing the ceramide inhibition of I(KCa). Taken together, our results show that, in rat pinealocytes, ceramide reduces the outward K(+) current predominantly by inhibiting I(KCa). Moreover, protein kinase C appears to be the main kinase involved in the ceramide inhibition of I(KCa).
Chik
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CL
Department of Physiology, Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada. cchik@ualberta.ca
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Karpinski
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D000818:Animals; D002518:Ceramides / Q000494:pharmacology*; D004553:Electric Conductivity; D007425:Intracellular Membranes / Q000502:physiology; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010870:Pineal Gland / Q000166:cytology / Q000378:metabolism*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated; D011493:Protein Kinase C / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D051381:Rats; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology
D002518:Ceramides; D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; C101954:N-caproylsphingosine; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D013108:Sphingomyelin Phosphodiesterase