Activation of a Ca2+-dependent K+ current in mouse fibroblasts by lysophosphatidic acid requires a pertussis toxin-sensitive G protein and Ras.
Lysophosphatidic acid (LPA) is a bioactive lipid that acts through G protein-coupled plasma membrane receptors and mediates a wide range of cellular responses. Here we report that LPA activates a K+ current in NIH3T3 mouse fibroblasts that leads to membrane hyperpolarization. The activation occurs with an EC50 value of 1.7 nM LPA. The K+ current is Ca2+-dependent, voltage-independent, and completely blocked by the K+ channel blockers charybdotoxin, margatoxin, and iberiotoxin with IC50 values of 1.7, 16, and 62 nM, respectively. The underlying K+ channels possess a single channel conductance of 33 pS in symmetrical K+ solution. Pretreatment of cells with pertussis toxin (PTX), Clostridium sordellii lethal toxin, or a farnesyl protein transferase inhibitor reduced the K+ current amplitude in response to LPA to about 25% of the control value. Incubation of cells with the protein tyrosine kinase inhibitor genistein or microinjection of the neutralizing anti-Ras monoclonal antibody Y13-259 reduced it by more than 50%. In contrast, the phospholipase C inhibitor U-73122 and the protein kinase A activator 8-bromo-cAMP had no effect. These results indicate that the K+ channel activation by LPA is mediated by a signal transduction pathway involving a PTX-sensitive G protein, a protein tyrosine kinase, and Ras. LPA is already known to activate Cl- channels in various cell types, thereby leading to membrane depolarization. In conjunction with our results that demonstrate LPA-induced membrane hyperpolarization by activation of K+ channels, LPA appears to be significantly involved in the regulation of the cellular membrane potential.
Repp
H
H
Rudolf-Buchheim-Institut für Pharmakologie, Justus-Liebig-Universität Giessen, Germany.
Koschinski
A
A
Decker
K
K
Dreyer
F
F
D016475:3T3 Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000187:drug effects* / Q000378:metabolism; D008246:Lysophospholipids / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D015203:Reproducibility of Results; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*; D018631:ras Proteins / Q000187:drug effects* / Q000378:metabolism
D008246:Lysophospholipids; D015221:Potassium Channels; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D018631:ras Proteins; D002118:Calcium