Non-Contractile Cells with Thin Processes Resembling Interstitial Cells of Cajal Found in the Wall of Guinea-Pig Mesenteric Arteries

Arterial interstitial cells of Cajal (ICC)-like cells (AIL cells) with a multipolar, irregular, elongated shape and with numerous thin (often less than 1 μm), sometimes branching, processes with lengths up to ≈60 μm were isolated enzymatically from 1st to 7th order branches of guinea-pig mesenteric artery. Some of the processes of AIL cells were growing (average speed ≈0.15 μm min⁻¹) and their growth was blocked by 10 μ M latrunculin B, an inhibitor of actin polymerisation. Staining with BODIPY phalloidin, a fluorescent dye selective for F-actin, showed the presence of F-actin in the processes of AIL cells. Voltage clamp of single AIL cells revealed an inward current that was four times more dense than in myocytes and was abolished by 10 μ M nicardipine, and an outward current carried exclusively by potassium ions that was reduced by 1 m M 4-aminopyridine and/or 100 n M iberiotoxin but unaffected by 10 n M dendrotoxin-K. Imaging of intracellular ionised calcium with fluo-4 using a laser scanning confocal microscope showed local or global 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 m M caffeine or 5 μ M 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. The presence of ICC-like cells is demonstrated for the first time in the media of resistance arteries.