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J Physiol Volume 575, Number 1, 191-200, August 15, 2006 DOI: 10.1113/jphysiol.2006.114116
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CARDIOVASCULAR

Altered energy transfer from mitochondria to sarcoplasmic reticulum after cytoarchitectural perturbations in mice hearts

James R. Wilding1,2, Frédéric Joubert1,2, Carla de Araujo1,2, Dominique Fortin1,2, Marta Novotova3, Vladimir Veksler1,2 and Renée Ventura-Clapier1,2

1 U-769 INSERM, Châtenay-Malabry, France
2 University Paris-Sud 11, 1FR 141, Faculty of Pharmacy, Châtenay-Malabry, France
3 Institute of Molecular Physiology & Genetics, Slovak Academy of Sciences, Bratislava, Slovak Republic

Sarcoplasmic reticulum (SR) calcium pump function requires a high local ATP/ADP ratio, which can be maintained by direct nucleotide channelling from mitochondria, and by SR-bound creatine kinase (CK)-catalysed phosphate-transfer from phosphocreatine. We hypothesized that SR calcium uptake supported by mitochondrial direct nucleotide channelling, but not bound CK, depends on the juxtaposition of these organelles. To test this, we studied a well-described model of cytoarchitectural disorganization, the muscle LIM protein (MLP)-null mouse heart. Subcellular organization was characterized using electron microscopy, and mitochondrial, SR and myofibrillar function were assessed in saponin-permeabilized fibres by measuring respiration rates and caffeine-induced tension transients. MLP-null hearts had fewer, less-tightly packed intermyofibrillar mitochondria, and more subsarcolemmal mitochondria. The apparent mitochondrial Km for ADP was significantly lower in the MLP-null heart than in control (175 ± 15 and 270 ± 33 µM, respectively), indicating greater ADP accessibility, although maximal respiration rate, mitochondrial content and total CK activity were unaltered. Active tension in the myofibres of MLP-null mice was 54% lower than in controls (39 ± 3 and 18 ± 1 mN mm–2, respectively), consistent with cytoarchitectural disorganization. SR calcium loading in the myofibres of MLP-null mice was similar to that in control myofibres when energy support was provided via Bound CK, but ~36% lower than controls when energy support was provided by mitochondrial (P < 0.05). Mitochondrial support for SR calcium uptake was also specifically decreased in the desmin-null heart, which is another model of cytoarchitectural perturbation. Thus, despite normal oxidative capacity, direct nucleotide channelling to the SR was impaired in MLP deficiency, concomitant with looser mitochondrial packing and increased nucleotide accessibility to this organelle. Changes in cytoarchitecture may therefore impair subcellular energy transfer and contribute to energetic and contractile dysfunction.

(Received 24 May 2006; accepted after revision 31 May 2006; first published online 1 June 2006)
Corresponding author R. Ventura-Clapier: U-769 INSERM, Faculté de Pharmacie, Université Paris-Sud, 5 rue J-B Clément, 92296 Châtenay-Malabry, France. Email: renee.ventura{at}cep.u-psud.fr






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