Cardiac inotropy, lusitropy, and Ca2+ handling with major metabolic substrates in rat heart

Abstract

Fatty acid (FA)-dependent oxidation is the predominant process for energy supply in normal heart. Impaired FA metabolism and metabolic insufficiency underlie the failing of the myocardium. So far, FA metabolism in normal cardiac physiology and heart failure remains undetermined. Here, we evaluate the mechanisms of FA and major metabolic substrates (termed NF) on the contraction, relaxation, and Ca2+ handling in rat left ventricular (LV) myocytes. Our results showed that NF significantly increased myocyte contraction and facilitated relaxation. Moreover, NF increased the amplitudes of diastolic and systolic Ca2+ transients ([Ca2+]i), abbreviated time constant of [Ca2+]i decay (tau), and prolonged the peak duration of [Ca2+]i. Whole-cell patch-clamp experiments revealed that NF increased Ca2+ influx via L-type Ca2+ channels (LTCC, ICa-integral) and prolonged the action potential duration (APD). Further analysis revealed that NF shifted the relaxation phase of sarcomere lengthening vs. [Ca2+]i trajectory to the right and increased [Ca2+]i for 50 % of sarcomere relengthening (EC50), suggesting myofilament Ca2+ desensitization. Butanedione monoxime (BDM), a myosin ATPase inhibitor that reduces myofilament Ca2+ sensitivity, abolished the NF-induced enhancement of [Ca2+]i amplitude and the tau of [Ca2+]i decay, indicating the association of myofilament Ca2+ desensitization with the changes in [Ca2+]i profile in NF. NF reduced intracellular pH ([pHi]). Increasing [pH]i buffer capacity with HCO3/CO2 attenuated Δ [pH]i and reversed myofilament Ca2+ desensitization and Ca2+ handling in NF. Collectively, greater Ca2+ influx through LTCCs and myofilament Ca2+ desensitization, via reducing [pH]i, are likely responsible for the positive inotropic and lusitropic effects of NF. Computer simulation recapitulated the effects of NF.Electronic supplementary materialThe online version of this article (doi:10.1007/s00424-016-1892-8) contains supplementary material, which is available to authorized users.

The Different Expression Patterns of HSP22, a Late Embryogenesis Abundant-like Protein, in Hypertrophic H9C2 Cells Induced by NaCl and Angiotensin II

“…This result suggests that HSP22 may participate in the protective process of cardiac hypertrophy with chronic hypernatremia and the protective process of intracellular Ca 2+ homeostasis. This agrees with our finding that the Ca 2+ in the hypertrophic H9C2 cells changed with the different HSP22 expression levels, because Ca 2+ is used as a second messenger in the heart, and Ca 2+ has important functions, including the regulation of metabolism, E-C coupling, and hypertrophic processes 43 44 45 46) . Our results indicate that HSP22 participates in the intracellular Ca 2+ homeostasis, because in our model, the impaired, intracellular free Ca 2+ homeostasis and an increased cell size were more evident with the decreased HSP22 expression than other for the groups.…”

Cardiac myosin binding protein-C palmitoylation is associated with increased myofilament affinity, reduced myofilament Ca2+ sensitivity and is increased in ischaemic heart failure

“…cMyBP-C palmitoylation had no significant effect on passive force (Supplementary Figure 2) or on the ability of the myofilaments to generate maximal force in saturating Ca 2+ (pCa4.5), however, there was a significant decreased in the maximal force generated in submaximal Ca 2+ (pCa6.0) suggesting a loss of Ca2+ sensitivity (Figure 2B). Increased cardiomyocyte fatty acid availability is associated with high fat diets, diabetes and insulin sensitivity (Zhao et al , 2018; Glatz, Luiken and Nabben, 2020) and at a cardiomyocyte level, treatment with high concentrations of palmitate or a mixture of fatty acids was associated with a reduction in peak sarcomere shortening and reduced myofilament calcium sensitivity which we suggest may be mediated in part by increased cMyBP-C palmitoylation (Angin et al , 2012; Zhao et al , 2016).…”

Functional Impact of Alternative Metabolic Substrates in Failing Human Cardiomyocytes

“… FFA: G/L/P + 200 μmol/L oleic acid (water soluble; Sigma O1257) + 100 μmol/L palmitic acid (BSA-conjugated; Sigma P0500) + 50 μmol/L L-carnitine + 100 μmol/L linoleic acid (water soluble; Sigma L5900). 13 3-OHB: G/L/P + 3 mmol/L (R)-(−)-3-hydroxybutyric acid sodium salt (Sigma 298360). 16 MIX: G/L/P + FFA + 3-OHB …”

“…FFA: G/L/P + 200 μmol/L oleic acid (water soluble; Sigma O1257) + 100 μmol/L palmitic acid (BSA-conjugated; Sigma P0500) + 50 μmol/L L-carnitine + 100 μmol/L linoleic acid (water soluble; Sigma L5900). 13 …”

“… 8 , 9 , 10 , 11 , 12 Despite the essential linkage between energy metabolism and contractility, only rare studies have used acute changes in cardiomyocytes contractility as a readout for evaluating the functional impact of changes in metabolic fuel utilization. 13 To address these gaps, we evaluated the effects of physiologic metabolic fuels on the contractility of cardiomyocytes isolated from human HFs and nonfailing hearts (NFs).…”