Products of heme-catalyzed transformation of the arachidonate derivative 12-HPETE open S-type K+ channels in Aplysia.
In Aplysia mechanosensory neurons, the neuropeptide FMRFamide increases the opening of the background S-K+ channel. This action is mediated by activation of arachidonic acid metabolism. Arachidonic acid in Aplysia nervous tissue is transformed through the 12-lipoxygenase pathway to 12-HPETE, which undergoes further metabolism. In intact sensory cells, 12-HPETE simulates the FMRFamide response, raising the question of whether 12-HPETE is the messenger molecule ultimately acting on the S-K+ channel. Here we show that in cell-free (inside-out) patches from sensory cells, 12-HPETE fails to modulate the S-K+ channel, but in the presence of hematin (which catalyzes 12-HPETE metabolism), it triggers sharp increases in the channel opening probability. We also found that SKF-525A, an inhibitor of the cytochrome P450, reduces the response to FMRFamide, arachidonic acid, and 12-HPETE in intact cells. We conclude that a heme-catalyzed transformation of 12-HPETE is necessary and sufficient to promote the opening of the S-K+ channel and a heme-containing enzyme such as cytochrome P450 might play this key role.
Belardetti
F
F
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235.
Campbell
W B
WB
Falck
J R
JR
Demontis
G
G
Rosolowsky
M
M
D000818:Animals; D001048:Aplysia; D001095:Arachidonic Acids / Q000494:pharmacology*; D002474:Cell-Free System; D019835:FMRFamide; D006418:Heme / Q000494:pharmacology*; D006427:Hemin / Q000494:pharmacology; D015289:Leukotrienes / Q000378:metabolism* / Q000494:pharmacology; D009479:Neuropeptides / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects*; D011725:Pyridines / Q000494:pharmacology
D001095:Arachidonic Acids; D015289:Leukotrienes; D009479:Neuropeptides; D015221:Potassium Channels; D011725:Pyridines; C013109:metapyrone; D006418:Heme; D019835:FMRFamide; C021201:12-HPETE; D006427:Hemin