Different cation sensitivities and binding site domains of Na+-Ca2+-K+ and Na+-Ca2+ exchangers

Cobalt chloride postconditioning as myoprotective therapy in cardiac ischemia-reperfusion

Since damage induced by ischemia-reperfusion (I/R) involves alterations in Ca²⁺ homeostasis and is reduced by ischemic postconditioning (IP) and that CoCl₂ can trigger changes resembling the response to a hypoxic event in normoxia and its blockade on Ca²⁺ current in heart muscle, our aim was to evaluate CoCl₂ as an IP therapeutic tool. Mechanic and energetic parameters of isolated and arterially perfused male Wistar rat heart ventricles were simultaneously analyzed in a model of I/R in which 0.23 mmol/L CoCl₂ was introduced upon reperfusion and kept or withdrawn after 20 min or introduced after 20 min of reperfusion. The presence of CoCl₂ did not affect diastolic pressure but increased post-ischemic contractile recovery, which peaked at 20 min and decreased at the end of reperfusion. This decrease was prevented when CoCl₂ was removed at 20 min of reperfusion. Total heat release increased throughout reperfusion, while economy increased between 15 and 25 min. No effect was observed when CoCl₂ was introduced at 20 min of reperfusion. In addition, both the area under the contracture curve evoked by 10 mmol/L caffeine-36 mmol/L Na⁺ and the contracture tension relaxation rate were higher with CoCl₂.Furthermore, CoCl₂ decreased the number of arrhythmias during reperfusion and the ventricular damaged area. The presence of CoCl₂ in reperfusion induces cardioprotection consistent with the improvement in cellular calcium handling. The use of CoCl₂ constitutes a potential cardioprotective tool of clinical relevance.

Cell culture alters Ca2+ entry pathways activated by store-depletion or hypoxia in canine pulmonary arterial smooth muscle cells

Previous studies have shown that, in acutely dispersed canine pulmonary artery smooth muscle cells (PASMCs), depletion of both functionally independent inositol 1,4,5-trisphosphate (IP(3))- and ryanodine-sensitive Ca(2+) stores activates capacitative Ca(2+) entry (CCE). The present study aimed to determine if cell culture modifies intracellular Ca(2+) stores and alters Ca(2+) entry pathways caused by store depletion and hypoxia in canine PASMCs. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured in fura 2-loaded cells. Mn(2+) quench of fura 2 signal was performed to study divalent cation entry, and the effects of hypoxia were examined under oxygen tension of 15-18 mmHg. In acutely isolated PASMCs, depletion of IP(3)-sensitive Ca(2+) stores with cyclopiazonic acid (CPA) did not affect initial caffeine-induced intracellular Ca(2+) transients but abolished 5-HT-induced Ca(2+) transients. In contrast, CPA significantly reduced caffeine- and 5-HT-induced Ca(2+) transients in cultured PASMCs. In cultured PASMCs, store depletion or hypoxia caused a transient followed by a sustained rise in [Ca(2+)](i). The transient rise in [Ca(2+)](i) was partially inhibited by nifedipine, whereas the nifedipine-insensitive transient rise in [Ca(2+)](i) was inhibited by KB-R7943, a selective inhibitor of reverse mode Na(+)/Ca(2+) exchanger (NCX). The nifedipine-insensitive sustained rise in [Ca(2+)](i) was inhibited by SKF-96365, Ni(2+), La(3+), and Gd(3+). In addition, store depletion or hypoxia increased the rate of Mn(2+) quench of fura 2 fluorescence that was also inhibited by these blockers, exhibiting pharmacological properties characteristic of CCE. We conclude that cell culture of canine PASMCs reorganizes IP(3) and ryanodine receptors into a common intracellular Ca(2+) compartment, and depletion of this store or hypoxia activates voltage-operated Ca(2+) entry, reverse mode NCX, and CCE.