Compartmental analysis of steady-state diaphragm Ca2+ kinetics in chronic congestive heart failure.
An analytic method based on simulation and modeling of long-term 45Ca(2+) efflux data was used to estimate steady-state Ca(2+) contents (nmolCa(2+)g(-1)tissuewetwt.) and exchange fluxes (nmolCa(2+)min(-1)g(-1)tissuewetwt.) for extracellular and intracellular compartments in in vitro resting diaphragm from congestive heart failure (CHF, n=12) and sham-operated (SHAM, n=10) rats. Left hemidiaphragms were excised from experimental animals, loaded with 45Ca(2+) for 1h, and washed out with 45Ca(2+)-free perfusate for 8h. Tissue from the right hemidiaphragm was used to assess single-fiber cross-sectional area (CSA) as well as the relative proteolytic activity of Ca(2+)-dependent calpain. Kinetic analysis of 45Ca(2+) efflux data revealed that CHF was associated with increased Ca(2+) contents of extracellular and intracellular compartments as well as increased Ca(2+) exchange fluxes for all compartments. This accounted for the model prediction of a 250% increase in total diaphragm Ca(2+). Furthermore, single-fiber CSA was decreased 12% and proteolytic activity of calpain was increased twofold in CHF diaphragm relative to SHAM.


CONCLUSIONS
The kinetic data are consistent with the hypothesis that diaphragm Ca(2+) overload in CHF required all intercompartmental Ca(2+) fluxes to increase. The potential relationships among Ca(2+) overload, increased activity of calpain, and wasting of the diaphragm in CHF are discussed.
Dominguez
Jesus F
JF
Department of Biokinesiology, University of Southern California, 1540 E. Alcazar Street, CHP-155, Los Angeles, CA 90089, USA. jdomingu@usc.edu
Howell
Sandra
S
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002154:Calpain / Q000378:metabolism; D002451:Cell Compartmentation / Q000187:drug effects / Q000502:physiology; D002908:Chronic Disease; D003964:Diaphragm / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D005110:Extracellular Space / Q000502:physiology; D006333:Heart Failure / Q000150:complications* / Q000378:metabolism / Q000503:physiopathology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D007424:Intracellular Fluid / Q000502:physiology; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D009133:Muscular Atrophy / Q000209:etiology* / Q000378:metabolism* / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar; D012120:Respiration Disorders / Q000209:etiology* / Q000378:metabolism* / Q000503:physiopathology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D002154:Calpain; D002118:Calcium