During an inflammatory process neutrophils get activated by cytokines, transmigrate the endothelium and migrate into affected tissue. The underlying signal transduction utilizes Ca²⁺ transients. To identify the involved Ca²⁺ entry channels we investigated the role of TRPC1 and TRPC6, members of the transient receptor potential (TRP) channel family.

The impact of TRPC1/TRPC6-deficiency on chemotaxis of murine neutrophils in 3-dimensional matrices was studied with time-lapse videomicroscopy. In chemotaxis assays fMLP (end-target chemoatractant) and KC/CXCL1 (intermediary chemoattractant) were applied. Intracellular Ca²⁺ concentration was analyzed with the fluorescent Ca²⁺-indicator Fura-2 and receptor signaling was studied via Western blot. Actin polymerization was determined by phalloidin staining.

Chemotaxis of TRPC1^-/- neutrophils in gradients of KC and fMLP was diminished. In contrast, fMLP-mediated chemotaxis of TRPC6^-/- neutrophils was unaffected while chemotaxis in gradients of KC was impaired. The chemotaxis defect of TRPC6^-/- neutrophils in KC gradients was accompanied by a diminished Ca²⁺ influx and decreased CXCR2 signaling. In contrast, fMLP stimulation in TRPC6^-/- cells led to a rise in Ca²⁺ influx that was undistinguishable from that in WT cells. Diminished Ca²⁺ transients after KC stimulation in TRPC6^-/- neutrophils was linked to reduced F-actin formation, while F-actin formation after fMLP stimulation was not affected by the loss of TRPC6.

Our findings indicate that TRPC1 and TRPC6 are important regulators in chemotaxis of murine neutrophils. TRPC6 is a component of intermediary chemoattractant-mediated actin polymerization but has no influence on end-target chemotaxis. In contrast, TRPC1 contributes to both, intermediary and end-target chemotaxis.