Multiple alterations in Ca2+ handling determine the negative staircase in a cellular heart failure model.
BACKGROUND
The flat or negative force frequency relationship (FFR) is a hallmark of the failing heart. Either decreases in SERCA2a expression, increases in Na(+)/Ca(2+) exchanger (NCX) expression or elevated Na(+)(i) have been independently proposed as mediators of the negative FFR.


RESULTS
To determine whether each one of these mechanisms is sufficient to account for the negative FFR of the failing heart or on the contrary, various mechanisms, acting in concert are required. SERCA2a was pharmacologically inhibited with thapsigargin (TG) or cyclopiazonic acid (CPA) or by using siRNA technology; Na(+)(i) was increased with either ouabain (Oua) or monensin and NCX protein was overexpressed by gene transfer (Ad.NCX), to mimic in nonfailing cat myocytes the phenotype of the failing heart and examine their effect on the FFR. The positive FFR of healthy myocytes remained unaffected after either SERCA2a inhibition, Na(+)(i) elevation, or NCX overexpression. However, the combination of TG + Oua, Oua + Ad.NCX, or TG + Ad.NCX, converted the positive FFR to negative. Moreover, the FFR became negative at lower frequencies, when the 3 interventions were combined.


CONCLUSIONS
Ca(2+) handling has to be altered at several levels to explain the negative FFR of the failing heart. These anomalies in Ca(2+) homeostasis acting in synergy have additive effects.
Palomeque
Julieta
J
Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata 1900, Argentina.
Petroff
Martin Vila
MV
Sapia
Luciana
L
Gende
Oscar A
OA
Mundiña-Weilenmann
Cecilia
C
Mattiazzi
Alicia
A
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002415:Cats; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D015870:Gene Expression; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology; D007211:Indoles / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism / Q000473:pathology*; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D034741:RNA, Small Interfering / Q000235:genetics; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007211:Indoles; D034741:RNA, Small Interfering; D019284:Thapsigargin; D012964:Sodium; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; C048960:indo-1; D002118:Calcium; C000543:cyclopiazonic acid