Ca2+ signaling in injured in situ endothelium of rat aorta.

Summary: The inner wall of excised rat aorta was scraped by a microelectrode and Ca²⁺ signals were investigated by fluorescence microscopy in endothelial cells (ECs) directly coupled with injured cells. The injury caused an immediate increase in the intracellular Ca²⁺ concentration ([Ca²⁺]_i), followed by a long-lasting decay phase due to Ca²⁺ influx from extracellular space. The immediate response was mainly due to activation of purinergic receptors, as shown by the effect of P_2X and P_2Y receptors agonists and antagonists, such as suramin, α,β-MeATP, MRS-2179 and 2-MeSAMP. Inhibition of store-operated Ca²⁺ influx did not affect either the peak response or the decay phase. Furthermore, the latter was: (i) insensitive to phospholipase C inhibition, (ii) sensitive to the gap junction blockers, palmitoleic acid, heptanol, octanol and oleamide, and (iii) sensitive to La³⁺ and Ni²⁺, but not to Gd³⁺. Finally, ethidium bromide or Lucifer Yellow did not enter ECs facing the scraped area. These results suggest that endothelium scraping: (i) causes a short-lasting stimulation of healthy ECs by extracellular nucleotides released from damaged cells and (ii) uncouples the hemichannels of the ECs facing the injury site; these hemichannels do not fully close and allow a long-lasting Ca²⁺ entry. [Copyright &y& Elsevier]