Relationship between calcium loading and impaired energy metabolism during Na+, K+ pump inhibition and metabolic inhibition in cultured neonatal rat cardiac myocytes.
This study tested the hypothesis that the initiating mechanism is a major determinant of the response to calcium (Ca) accumulation in myocardium. Cultured neonatal rat ventriculocytes were exposed to Na+, K+ pump inhibition with 1 mM ouabain and metabolic inhibition with 20 mM 2-deoxy-D-glucose and 1 mM cyanide (DOG-CN) for up to 2 h. Microspectrofluorometry of myocytes loaded with fura-2 showed that ouabain resulted in a relatively rapid increase in [Ca2+]i up to 2-3 microM (two to threefold above peak systolic level) and that DOG-CN produced an initial decrease and then a relatively slow increase in [Ca2+]i up to peak systolic level. Electron probe x-ray microanalysis (EPMA) showed prominent increases in Na and Ca and decreases in K and Mg in cytoplasm and mitochondria with both interventions, although the increases in Ca were greater with ouabain than DOG-CN. ATP was reduced by 58% after 1 and 2 h of ouabain and by 70 and 90% after 1 and 2 h of DOG-CN, respectively. Thus, ouabain produced greater calcium accumulation and less ATP reduction than DOG-CN. Upon return to normal medium for 30 min, myocytes showed recovery of most electrolyte alterations and resumption of normal Ca2+ transients after 1 h exposure to either ouabain or DOG-CN; however, recovery was less after 2 h of either treatment, with elevated [Ca2+]i maintained in many myocytes. We conclude that the severity of myocyte injury is influenced by the magnitude and duration of both ATP reduction and calcium accumulation.
Morris
A C
AC
Department of Pathology, University of Texas Southwestern Medical Center, Dallas 75235-9072.
Hagler
H K
HK
Willerson
J T
JT
Buja
L M
LM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D003486:Cyanides; D003847:Deoxyglucose; D004577:Electron Probe Microanalysis; D004734:Energy Metabolism / Q000187:drug effects*; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D010042:Ouabain; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D051381:Rats; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology
D003486:Cyanides; D015221:Potassium Channels; D015222:Sodium Channels; D010042:Ouabain; D000255:Adenosine Triphosphate; D003847:Deoxyglucose; D002118:Calcium