Cells similar to the interstitial cells of Cajal (ICCs) were reported in lymphatic vessels (McCloskey et al. 2002) and portal vein (Povstyan et al. 2003). This work describes the morphology, calcium dynamics and immunohistochemistry of non-contractile cells with thin processes, named arterial ICC-like (AIL) cells, found in enzymic dispersions of arteries.

Guinea-pigs were humanely killed by cervical dislocation followed by exsanguination. Single cells were obtained by enzymic digestion of mesenteric arteries, loaded with a calcium sensitive fluorescent dye and imaged using a laser scanning confocal microscope. In some experiments the cells were voltage-clamped to record membrane current simultaneously with cell imaging. In immunohistochemical experiments the cells were fixed, and incubated with primary antibodies against a target molecule and then with fluorescent secondary antibodies.

AIL cells had an irregular elongated shape and numerous thin (often less than 1 µm wide) processes with lengths up to ~60 µm. Some of the processes were observed to grow in length (average speed ~0.15 µm min^-1) and this elongation was blocked by 10 µM latrunculin B, an inhibitor of actin polymerization. Staining with BODIPY phalloidin, a fluorescent dye selective for F-actin, showed F-actin to be present in the processes of AIL cells. Imaging of intracellular ionised calcium with fluo-4 using a laser scanning confocal microscope showed global or local calcium transients lasting several seconds in ~28 % of AIL cells. When membrane current was recorded simultaneously, the calcium transients were found to correspond to long-lasting transient outward currents, which occurred at potentials positive to -40 mV. Unlike myocytes, AIL cells did not contract in response to 1 mM caffeine or 5 µM noradrenaline, although they responded with a [Ca²⁺]_i increase. The segments of intact arteries did not stain for c-kit, a marker of ICCs. Single AIL cells stained positive for vimentin, desmin and smooth muscle myosin, suggesting their close relationship to smooth muscle. However, the numerous processes and lack of contractile ability suggest they have some specialised function.

This work was supported by a British Heart Foundation Programme Grant RG 99001 and The Wellcome Trust grant 042293.