Abstract
The data presented in this work suggest that in human umbilical artery (HUA) smooth muscle cells, the Na +/Ca 2+ exchanger (NCX) is active and working in the reverse mode. This supposition is based on the following results: (i) microfluorimetry in HUA smooth muscle cells in situ showed that a Ca 2+-free extracellular solution diminished intracellular Ca 2+ ([Ca 2+] i), and KB-R7943 (5 μM), a specific inhibitor of the Ca 2+ entry mode of the exchanger, also decreased [Ca 2+] i (40.6 ± 4.5% of Ca 2+-free effect); (ii) KB-R7943 produced the relaxation of HUA rings (−24.7 ± 7.3 gF/gW, n = 8, p < 0.05); (iii) stimulation of the NCX by lowering extracellular Na + increases basal [Ca 2+] i proportionally to Na + reduction (Δ fluorescence ratio = 0.593 ± 0.141 for Na +-free solution, n = 8) and HUA rings’ contraction (peak force = 181.5 ± 39.7 for 130 mM reduction, n = 8), both inhibited by KB-R7943 and a Ca 2+-free extracellular solution. In conclusion, the NCX represents an important Ca 2+ entry route in HUA smooth muscle cells.
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