Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Systolic heart failure (HF) is characterized by reduced systolic function and often by arrhythmias. We studied a rabbit model of HF (induced by combined aortic insufficiency and stenosis) which shows both contractile dysfunction and arrhythmogenesis. In this model we find an approximately 100% increase in Na/Ca exchange (NaCaX) expression at the level of mRNA, protein and function, but only a modest decrease in SR Ca-ATPase (approximately 24%, only detectable in cellular function). This combination results in a 40% reduction in SR Ca content in HF, which is sufficient to explain the 40% reduction in twitch Ca transients and 30-38% decrease in contractile function in this HF model. When stimulated by isoproterenol the SR Ca load readily reaches the threshold for spontaneous SR Ca release (this threshold Ca load is unchanged in HF). This SR Ca release activates a transient inward current (I(ti)) carried exclusively by NaCaX. For a given SR Ca release there is greater I(ti) in HF (due to higher NaCaX). We also find a 49% decrease in the inward rectifier potassium current (I(K1)), which allows greater depolarization for a given I(ti). Thus, higher NaCaX and lower I(K1) greatly increase the likelihood that an SR Ca release-induced delayed afterdepolarization (DAD) will trigger an arrhythmogenic action potential. We conclude that NaCaX contributes in major ways to both contractile dysfunction (by reducing SR Ca) and increased propensity for triggered arrhythmias (by increasing I(ti) and DADs).
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PMID:Upregulated Na/Ca exchange is involved in both contractile dysfunction and arrhythmogenesis in heart failure. 1247 32

Systolic heart failure may be due to too few cardiomyocytes, or to reduced contractile function of the heart cells. In the latter situation the myocardial function is impaired and this condition is called myocardial failure. The pathophysiological mechanism behind this cellular defect is not known, but Ca2+ handling is altered. Although the most important trigger of sarcoplasmatic reticulum (SR) Ca2+ release, the L-type Ca2+ current, seems to be unaltered, SR Ca2+ load is reduced in human heart failure. This could explain the reduced contractility observed in failing hearts. Three possible mechanisms have been suggested to explain the reduction in SR Ca2+ load. They are leak through the SR Ca2+ release channel (RyR), impaired SR Ca2+ ATPase (SERCA) function and increased Na+/Ca2+-exchanger (NCX) function. Leak through RyR is not consistently found. Increased NCX function is probably secondary to a change in Ca2+ handling, and thus not a primary mechanism, but blockade of the NCX might have therapeutic potential. Reduced SERCA function is probably a primary mechanism for the observed systolic dysfunction, and further insight is to be gained through studies in genetically modified models.
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PMID:EC-coupling in normal and failing hearts. 1609 9