title: Transport of Ca2+ from sarcoplasmic reticulum to mitochondria in rat ventricular myocytes.
abstract: Studies with electron microscopy have shown that sarcoplasmic reticulum (SR) and mitochondria locate close to each other in cardiac muscle cells. We investigated the hypothesis that this proximity results in a transient exposure of mitochondrial Ca2+ uniporter (CaUP) to high concentrations of Ca2+ following Ca2+ release from the SR and thus an influx of Ca2+ into mitochondria. Single ventricular myocytes of rat were skinned by exposing them to a physiological solution containing saponin (0.2 mg/ml). Cytosolic Ca2+ concentration ([Ca2+]c) and mitochondrial Ca2+ concentration ([Ca2+]m) were measured with fura-2 and rhod2, respectively. Application of caffeine (10 mM) induced a concomitant increase in [Ca2+]c and [Ca2+]m. Ruthenium red, at concentrations that block CaUP but not SR release, diminished the caffeine-induced increase in [Ca2+]m but not [Ca2+]c. In the presence of 1 mM BAPTA, a Ca2+ chelator, the caffeine-induced increase in [Ca2+]m was reduced substantially less than [Ca2+]c. Moreover, inhibition of SR Ca2+ pump with two different concentrations of thapsigargin caused an increase in [Ca2+]m, which was related to the rate of [Ca2+]c increase. Finally, electron microscopy showed that sites of junctions between SR and T tubules from which Ca2+ is released, or Ca2+ release units, CRUs, are preferentially located in close proximity to mitochondria. The distance between individual SR Ca2+ release channels (feet or ryanodine receptors) is very short, ranging between approximately 37 and 270 nm. These results are consistent with the idea that there is a preferential coupling of Ca2+ transport from SR to mitochondria in cardiac muscle cells, because of their structural proximity.
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, New York 14642, USA.
authors.forename: V K
authors.initials: VK
authors.lastname: Sharma
authors.forename: V
authors.initials: V
authors.lastname: Ramesh
authors.forename: C
authors.initials: C
authors.lastname: Franzini-Armstrong
authors.forename: S S
authors.initials: SS
authors.lastname: Sheu
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D006352:Heart Ventricles; D007700:Kinetics; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D002614:Chelating Agents; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium