title: Effect of osmotic stress on spontaneous calcium sparks in rat ventricular myocytes.
abstract: OBJECTIVE
  To study whether the volume of cardiomyocytes and their functions would change under severe pathological conditions or osmotic stress. To clarify the role of ryanodine receptors/calcium release channels (RyRs) in the functional change, the effect of osmotic stress on spontaneous Ca2+ sparks in rat ventricular myocytes was investigated.
  
  
  METHODS
  A laser scanning confocal microscope was used to detect spontaneous Ca2+ sparks of intact or saponin permeabilized myocytes loaded with Fluo-4. High and low tonicity was obtained by adding sucrose and reducing NaCl concentration in the external medium, respectively.
  
  
  RESULTS
  In intact myocytes the frequency of Ca2+ sparks was increased and decreased by hyperosmotic (1.5 T) and hyposmotic (0.6 T) exposure, respectively. In addition, hyperosmotic exposure increased the temporal parameters and decreased the spatial parameter of Ca2+ sparks, while opposite changes occurred with hyposmotic exposure. The spatio-temporal properties of Ca2+ sparks were slightly affected by altering [K+]i (50-200 mmol/L) in saponin permeabilized myocytes in the presence of 8% dextran. It was observed that the spatio-temporal parameters of the Ca2+ sparks in permeabilized myocytes were dose-dependently altered by dextran. The propagating velocity of Ca2+ waves in intact and permeabilized myocyte was also affected by osmotic pressure or dextran.
  
  
  CONCLUSIONS
  The effect of osmotic stress on the frequency of spontaneous Ca2+ sparks might be ascribed to the change of myoplasmic Ca2+ and Ca2+ content in the sarcoplasmic reticulum, while the effect on the spatio-temporal properties is caused by the alteration of Ca2+ diffusion mainly resulting from the morphological change of the myocytes.
authors.affiliation: Unit of Cell Signal Transduction, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Xie
authors.forename: Pei-hong
authors.initials: PH
authors.lastname: Zhu
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002469:Cell Separation; D003911:Dextrans / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006352:Heart Ventricles / Q000166:cytology; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D009997:Osmotic Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
chemical_list: D003911:Dextrans; D001224:Aspartic Acid; D002110:Caffeine; D002118:Calcium