The intracellular calcium concentration plays an important role in the (directed) migration of neutrophil granulocytes (PMNs). When exposed to a chemical gradient of chemoattractants, such as those encountered in the vicinity of a site of inflammation, changes of the intracellular calcium concentration are crucial for turning this chemotactic information into directed migration. Transient Receptor Potential (TRP) channels are calcium permeable cation channels that that are crucially involved in this process. Different activation mechanisms for these channels are under discussion, such as receptor operated calcium entry (ROCE), store operated calcium entry (SOCE) or direct mechanical stimulation. Here we investigated the role of TRPC1 channels in PMN stimulation with a murine knockout model.

Bone marrow-derived PMNs were stimulated with N-Formylmethionyl-leucyl-phenylalanine (fMLP), a common end-target chemoattractant. The intracellular calcium concentration was measured with the fluorescent dye fura-2.

Using a gaussian filter calcium maps could be created, visualizing the intracellular calcium distribution in PMNs over space and time. These may provide hints about the consequences of the changed calcium distribution in the presence and absence of TRPC1 concerning migration speed and directionality.

Surprisingly, the rise of the intracellular calcium concentration elicited by fMLP was more pronounced in TRPC1-/- than in WT PMNs.

To differentiate between store-release and trans-membraneous calcium entry, additional measurements with calcium-free medium were performed and the manganese quenching method was applied. These experiments consistently showed that the augmented calcium response in TRPC1-/- PMNs was due to an increased calcium influx from the extracellular space.

Thus, TRPC1 channels normally attenuate fMLP-triggered calcium influx.