Activation of a Ca2+-dependent K+ current in mouse fibroblasts by sphingosine-1-phosphate involves the protein tyrosine kinase c-Src.

Sphingosine-1-phosphate (S1P) is a phospholipid that acts through G-protein-coupled plasma membrane receptors and induces a broad spectrum of cellular responses, including proliferation, migration, differentiation and apoptosis. Here we report that in NIH3T3 and C3H10T1/2 mouse fibroblasts S1P activates a Ca2+-dependent, voltage-independent K+ current (EC50-value 113 nM) that is blocked by the K+ channel blockers charybdotoxin, margatoxin, and iberiotoxin. The K+ current activation by S1P is transient and leads to a large membrane hyperpolarization. Recently, we showed that lysophosphatidic acid (LPA), a serum lipid with similar biological effects compared to those of S1P, can activate a Ca2+-dependent K+ current in NIH3T3 cells that has identical properties compared to the one that is activated by S1P. When applied consecutively, both S1P and LPA induced a K+ current response in NIH3T3 cells, which indicates that the K+ current activation is not subjected to cross-desensitization between S1P and LPA. In C3H10T1/2 mouse fibroblasts that overexpress the nonreceptor protein tyrosine kinase c-Src, the amplitude of the S1P-induced K+ current was almost doubled compared to the one that we found in control cells. Expression of a non-myristylated c-Src mutant led to a further increase in the K+ current response to S1P, whereas expression of a kinase-defective c-Src mutant reduced it to about 40% compared to the control value. Our data show that S1P activates Ca2+-dependent K+ channels in mouse fibroblasts via an intracellular signalling pathway that involves the non-receptor protein tyrosine kinase c-Src.