Publications

• Na(+)-dependent Ca2+ efflux mechanism of heart mitochondria is not a passive Ca2+/2Na+ exchanger.

  Baysal K., Jung D.W., Gunter K.K., Gunter T.E., Brierley G.P.

  Net Ca2+ flux across the inner membrane of respiring heart mitochondria was evaluated under conditions in which virtually all Ca2+ movement can be attributed to the Na+/Ca2+ antiport. If this antiport promotes a passive electroneutral exchange of Ca2+ for 2Na+, the Ca2+ gradient should be equal to ... >> More

  Net Ca2+ flux across the inner membrane of respiring heart mitochondria was evaluated under conditions in which virtually all Ca2+ movement can be attributed to the Na+/Ca2+ antiport. If this antiport promotes a passive electroneutral exchange of Ca2+ for 2Na+, the Ca2+ gradient should be equal to the square of the Na+ gradient at equilibrium. Because the mitochondrial Na+/H+ antiport equilibrates the Na+ and H+ gradients, the Ca2+ gradient should also equal the square of the H+ gradient. In a series of > 20 determinations at different matrix [Ca2+], different delta pH, and varying membrane potential, it was found that Ca2+ is transported out of the mitochondrion against gradients from 15-to 100-fold greater than the value predicted for passive electroneutral exchange. It is concluded that the observed gradients are too large to be sustained by passive Ca2+/2Na+ exchange. The observed gradients are compatible with an electrogenic Ca2+/3Na+ exchange. Alternatively another source of energy is available to support these gradients. << Less

  Am J Physiol 266:C800-8(1994) [PubMed] [EuropePMC]

• Mitochondria control store-operated Ca(2+) entry through Na(+) and redox signals.

  Ben-Kasus Nissim T., Zhang X., Elazar A., Roy S., Stolwijk J.A., Zhou Y., Motiani R.K., Gueguinou M., Hempel N., Hershfinkel M., Gill D.L., Trebak M., Sekler I.

  Mitochondria exert important control over plasma membrane (PM) Orai1 channels mediating store-operated Ca²⁺ entry (SOCE). Although the sensing of endoplasmic reticulum (ER) Ca²⁺ stores by STIM proteins and coupling to Orai1 channels is well understood, how mitochondria commun ... >> More

  Mitochondria exert important control over plasma membrane (PM) Orai1 channels mediating store-operated Ca²⁺ entry (SOCE). Although the sensing of endoplasmic reticulum (ER) Ca²⁺ stores by STIM proteins and coupling to Orai1 channels is well understood, how mitochondria communicate with Orai1 channels to regulate SOCE activation remains elusive. Here, we reveal that SOCE is accompanied by a rise in cytosolic Na⁺ that is critical in activating the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX) causing enhanced mitochondrial Na⁺ uptake and Ca²⁺ efflux. Omission of extracellular Na⁺ prevents the cytosolic Na⁺ rise, inhibits NCLX activity, and impairs SOCE and Orai1 channel current. We show further that SOCE activates a mitochondrial redox transient which is dependent on NCLX and is required for preventing Orai1 inactivation through oxidation of a critical cysteine (Cys195) in the third transmembrane helix of Orai1. We show that mitochondrial targeting of catalase is sufficient to rescue redox transients, SOCE, and Orai1 currents in NCLX-deficient cells. Our findings identify a hitherto unknown NCLX-mediated pathway that coordinates Na⁺ and Ca²⁺ signals to effect mitochondrial redox control over SOCE. << Less

  EMBO J. 36:797-815(2017) [PubMed] [EuropePMC]

• Gram-negative endotoxemia: effects on cardiac Na-Ca exchange and stoichiometry.

  Hale C.C., Allert J.A., Keller R.S., Adams H.R., Parker J.L.

  We studied the acute effects of gram-negative endotoxemia on Na-Ca exchange activity and stoichiometry in cardiac sarcolemmal (SL) vesicles isolated from pentobarbital-anesthetized dogs. Dogs were given either endotoxin (ET; 1.5 mg/kg IV) or saline vehicle (C; n = 4 dogs/group). Characteristic of ... >> More

  We studied the acute effects of gram-negative endotoxemia on Na-Ca exchange activity and stoichiometry in cardiac sarcolemmal (SL) vesicles isolated from pentobarbital-anesthetized dogs. Dogs were given either endotoxin (ET; 1.5 mg/kg IV) or saline vehicle (C; n = 4 dogs/group). Characteristic of endotoxemia, endotoxin produced a decrease in mean arterial pressure from 120 to 60 mmHg, an increase in packed cell volume from 38% to 60%, and an increase in heart rate from 130 to 190 bpm. After 2 hr, hearts were removed and SL vesicles were prepared from left and right ventricular tissue. For ET and C, Na-dependent Ca2+ uptake (left ventricle) was 3.13 and 3.44 (2 sec) and 18.60 and 19.42 (60 sec) nmole Ca2+/mg protein, respectively; ET group values were not significantly different from corresponding C values in either left or right ventricles. The stoichiometry of Na-Ca exchange was determined in left ventricular vesicles by a previously described thermodynamic approach utilizing a K+-valinomycin gradient opposed by Na+ equilibrium potentials (Reeves and Hale: J Biol Chem 259:7733-7739, 1984). The stoichiometry of exchange of Na+ for Ca2+ was 2.84 +/-0.09 and 2.74 +/-0.14 for ET and C, respectively. We conclude that during the developmental phase (2 hr) of endotoxemia, there were no ET-mediated changes in cardiac Na-Ca exchange activity in SL vesicles from either left or right ventricular tissue and the exchange process remained electrogenic with a stoichiometry of 3Na+ for 1Ca2+. << Less

  Circ Shock 29:133-142(1989) [PubMed] [EuropePMC]