title: Enhanced cell volume regulation: a key protective mechanism of ischemic preconditioning in rabbit ventricular myocytes.
abstract: Accumulation of osmotically active metabolites, which create an osmotic gradient estimated at ~60 mOsM, and cell swelling are prominent features of ischemic myocardial cell death. This study tests the hypothesis that reduction of ischemic swelling by enhanced cell volume regulation is a key mechanism in the delay of ischemic myocardial cell death by ischemic preconditioning (IPC). Experimental protocols address whether: (i) IPC triggers a cell volume regulation mechanism that reduces cardiomyocyte swelling during subsequent index ischemia; (ii) this reduction in ischemic cell swelling is sufficient in magnitude to account for the IPC protection; (iii) the molecular mechanism that mediates IPC also mediates cell volume regulation. Two experimental models with rabbit ventricular myocytes were studied: freshly isolated pelleted myocytes and 48-h cultured myocytes. Myocytes were preconditioned either by distinct short simulated ischemia (SI)/simulated reperfusion protocols (IPC), or by subjecting myocytes to a pharmacological preconditioning (PPC) protocol (1 microM calyculin A, or 1 microM N(6)-2-(4-aminophenyl)ethyladenosine (APNEA), prior to subjecting them to either different durations of long SI or 30 min hypo-osmotic stress. Cell death (percent blue square myocytes) was monitored by trypan blue staining. Cell swelling was determined by either the bromododecane cell flotation assay (qualitative) or video/confocal microscopy (quantitative). Simulated ischemia induced myocyte swelling in both the models. In pelleted myocytes, IPC or PPC with either calyculin A or APNEA produced a marked reduction of ischemic cell swelling as determined by the cell floatation assay. In cultured myocytes, IPC substantially reduced ischemic cell swelling (P < 0.001). This IPC effect on ischemic cell swelling was related to an IPC and PPC (with APNEA) mediated triggering of cell volume regulatory decrease (RVD). IPC and APNEA also significantly (P < 0.001) reduced hypo-osmotic cell swelling. This IPC and APNEA effect was blocked by either adenosine receptor, PKC or Cl(-) channel inhibition. The osmolar equivalent for IPC protection approximated 50-60 mOsM, an osmotic gradient similar to the estimated ischemic osmotic load for preconditioned and non-preconditioned myocytes. The results suggest that cell volume regulation is a key mechanism that accounts for most of the IPC protection in cardiomyocytes.
authors.affiliation: Division of Cardiovascular Research, Research Institute, The Hospital for Sick Children, Ont., Toronto, Canada. diazport@sickkids.on.ca
authors.forename: Roberto J
authors.initials: RJ
authors.lastname: Diaz
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Armstrong
authors.forename: Michelle
authors.initials: M
authors.lastname: Batthish
authors.forename: Peter H
authors.initials: PH
authors.lastname: Backx
authors.forename: Charles E
authors.initials: CE
authors.lastname: Ganote
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Wilson
mesh_terms: D000818:Animals; D048429:Cell Size / Q000502:physiology; D006321:Heart / Q000502:physiology*; D019194:Ischemic Preconditioning; D032383:Myocytes, Cardiac / Q000166:cytology*; D011817:Rabbits