Sodium-Dependent Calcium Release from Vascular Smooth Muscle Mitochondria.

Abstract

Interest in mitochondrial calcium (Ca2+) uptake and release waned as it became apparent that sarcoplasmic reticulum calcium stores dominate the control of cytoplasmic calcium concentration.Our recent demonstration of a very large rise in vascular smooth muscle (VSM) cytoplasmic sodium (Na+) concentration after inhibition of the sodium, potassium-ATPase (sodium pump) led us to several questions. Do VSM mitochondria show Na+-dependent Ca2+ release? Are the documented changes in cytoplasmic Na+ concentration sufficient to cause Ca2+ release? Do features of the cardiac mitochondrial exchange system, including differential sensitivity to a number of calcium antagonists and cation specificity, apply to VSM?We isolated mitochondria from bovine aorta and mesenteric arteries and employed arsenazo III as the Ca2+ indicator. Mitochondria from arterial vessels accumulated added calcium (up to 50 nmol Ca2+/mg protein) and released Ca2+ on exposure to Na+. This concentration-dependent relationship was linear from 0 to 10 mM of Nat, and it plateaued between 20 mM and 40 mM of Nat. VSM mitochondria exposed to 20 mM Na+ released 118±25 nmol Ca2+ per mg mitochondrial protein in 20 min, when a new equilibrium was reached. Lithium (Li+), in contrast to Na+, produced much smaller amounts of Ca2+ release from the VSM mitochondria. Na+-dependent Ca2+ release was antagonized in a concentration-dependent manner by diltiazem (0-320 pM) with a Ki of 10.2 hM. Nifedipine had a lesser effect, and verapamil produced almost no inhibition. VSM mitochondria responses resemble those from heart mitochondria in that Na+-dependent Ca2+ release is present with a similar range of sensitivity to Na+ and a similar pattern of influence of diltiazem, nifedipine and verapamil. However, the influence of Li+ on Ca2+ release was much smaller and the amount of the Ca2+ released was much greater for VSM mitochondria compared with that reported for heart mitochondria. The large amount of Ca2+ released and the range of Na+ concentration that provoked Ca2+ release being within the physiologically achievable range raise the interesting possibility that these mechanisms may modify intramitochondrial cytosolic Ca2+ concentration, and hence could potentially contribute to the contractile response that follows inhibition of the sodium pump. (Hypertens Res 2000; 23: 39-45)

The short variant of optic atrophy 1 (OPA1) improves cell survival under oxidative stress

“…Thapsigargin (1 µM) was added to inhibit ER Ca 2+ uptake. The Ca 2+ indicator arsenazo III (100 µM) was added, and kinetic measurements of absorbance were performed at 650 nm (reference at 685 nm) (76)(77)(78). After one minute, 40 µM CaCl2 was added at every 2 minutes until no further Ca 2+ uptake was observed.…”

Mitochondrial calcium cycling in neuronal function and neurodegeneration

“…Despite the appreciation of NCLX as a mediator of Ca 2+ extrusion from mitochondria, several studies showed that NCLX is also localized on the plasma membrane, endoplasmic reticulum (ER), and possibly other organelles ( Haworth and Hunter, 1979 ; Bernardi, 1999 ; Cai and Lytton, 2004a ; Palty et al, 2004 ; Palty et al, 2006 ; Han et al, 2015 ; Rysted et al, 2021 ). There is also inconsistency between the ability of NCLX to exchange Ca 2+ for Li + nearly as effectively as for Na + ( Palty et al, 2004 ; Roy et al, 2017 ) and the observations that Li + -driven mitochondrial Ca 2+ efflux is only 10–25% of that driven by Na + ( Crompton et al, 1977 ; Tokunaga et al, 2000 ; Rysted et al, 2021 ). In addition, recent studies showed that NCLX knockdown or knockout had little effect on mitochondrial Ca 2+ extrusion in airways smooth muscle and B lymphocytes, respectively ( Emrich et al, 2022 ; Johnson et al, 2022 ).…”