Iodinated radiographic contrast media inhibit the capacitative calcium entry into smooth muscle cells of the swine renal artery

RATIONALE AND OBJECTIVES. To investigate whether nonionic, iodinated, radiographic contrast media (RCM) could modulate calcium release from or calcium entry into smooth muscle cells of the swine renal artery. METHODS. Intracellular calcium concentrations of isolated myocytes loaded with the calcium-sensitive dye fluo-3 were analyzed using a fluorescence imaging system. Calcium signals were compared with isometric contractions of vascular segments in an organ bath. The effects of the triiodinated monomer iomeprol were compared with those of a mannitol solution. RESULTS. Stimulation of a-receptors by phenylephrine caused a biphasic calcium signal. Transient liberation of calcium from intracellular stores triggered the sustained entry of extracellular calcium (capacitative entry). Iomeprol and mannitol slightly inhibited the initial transient spike to the same extent. The calcium influx was reversibly inhibited by RCM by about 50%. Up to a concentration of 40 mmol/L, the inhibition induced by iomeprol was significantly higher than that induced by mannitol (P < 0.05-0.01). In isolated arterial segments, relaxation of the contraction phase depending on the calcium influx was significantly higher with the RCM than with mannitol (P < 0.01). CONCLUSIONS. Vasodilatation by CM is associated with a reduction in the capacitative entry of calcium. The mechanism of this effect is not clear, but it can be ruled out that it is mainly due to the high osmolarity of these compounds.