Activation of a Ca2+-dependent K+ current in mouse fibroblasts by lysophosphatidic acid requires a pertussis toxin-sensitive G protein and Ras

Abstract

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.