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The heart manifests hypertrophic growth in response to elevation of afterload pressure. Cardiac myocyte growth involves new protein synthesis and membrane expansion, of which a number of cellular quality control machineries are stimulated to maintain function and homeostasis. The unfolded protein response is potently induced during cardiac hypertrophy to enhance protein-folding capacity and eliminate terminally misfolded proteins. However, whether the unfolded protein response directly regulates cardiac myocyte growth remains to be fully determined. Here, we show that GRP78 (glucose-regulated protein of 78 kDa)-an endoplasmic reticulum-resident chaperone and a critical unfolded protein response regulator-is induced by cardiac hypertrophy. Importantly, overexpression of GRP78 in cardiomyocytes is sufficient to potentiate hypertrophic stimulus-triggered growth. At the in vivo level, TG (transgenic) hearts overexpressing GRP78 mount elevated hypertrophic growth in response to pressure overload. We went further to show that GRP78 increases GATA4 (GATA-binding protein 4) level, which may stimulate Anf (atrial natriuretic factor) expression and promote cardiac hypertrophic growth. Silencing of GATA4 in cultured neonatal rat ventricular myocytes significantly diminishes GRP78-mediated growth response. Our results, therefore, reveal that protein-folding chaperone GRP78 may directly enhance cardiomyocyte growth by stimulating cardiac-specific transcriptional factor GATA4. [ABSTRACT FROM AUTHOR]

The article presents a study which dealt with the changes in the cardiac function as well as L-type calcium current in the left ventricle of a knockout mouse. The researchers used the patch-clamp approach to record the alterations in the L-type calcium in ventricular myocytes. They found that cardiac function and the stimulation of ß-adrenergic are contributing factors to the heart rate.

Abstract: Purpose: This study aimed to develop and validate a model for prediction of septic shock in neonates with sepsis. Materials and methods: This retrospective study included early-onset septic neonates in the Renmin Hospital of Wuhan University between January 2017 and June 2021. The neonates were divided into the training set and the validation set in a ratio of 7:3 and further categorized into septic shock group and none-shock group according to presence or absence of shock symptoms. Results: A total of 406 septic neonates were enrolled, including 217 in septic shock group. Sex (odds ratio [OR] = 0.092, 95% confidence interval [CI]: 0.012 to 0.683, P = 0.020), C-reactive protein at 6 h (OR = 8.475, 95% CI: 3.154 to 22.774, P < 0.001), serum amyloid A at 6 h (OR = 1.179, 95% CI: 1.094 to 1.269, P < 0.01), white blood cells at 6 h (OR = 0.173, 95% CI: 0.092 to 0.326, P < 0.001), platelets at 6 h (OR = 0.985, 95% CI: 0.975 to 0.995, P < 0.001), and Ca 2+ at 6 h (OR = 1.44 × 10 11 , 95% CI: 2.70 × 10 6 to 7.70 × 10 15 , P < 0.001) were identified as independent risk factors for septic shock and were further included in the nomogram. The areas under the receiver operator characteristic curve were 0.873 and 0.920 in training and validation sets, respectively. Conclusions: A predictive model for early diagnosis of septic shock in neonates was developed and initially validated in this study, allowing for timely intervention., Competing Interests: The authors report no conflicts of interest., (Copyright © 2024 by the Shock Society.)

Rationale: Recent studies have highlighted important roles of CaMKII in regulating Ca(2+) handling and excitation-contraction coupling. However, the cardiac effect of chronic CaMKII inhibition has not been well understood., Objective: We have tested the alterations of L-type calcium current (I(Ca)) and cardiac function in CaMKIIdelta knockout (KO) mouse left ventricle (LV)., Methods and Results: We used the patch-clamp method to record I(Ca) in ventricular myocytes and found that in KO LV, basal I(Ca) was significantly increased without changing the transmural gradient of I(Ca) distribution. Substitution of Ba(2+) for Ca(2+) showed similar increase in I(Ba). There was no change in the voltage dependence of I(Ca) activation and inactivation. I(Ca) recovery from inactivation, however, was significantly slowed. In KO LV, the Ca(2+)-dependent I(Ca) facilitation (CDF) and I(Ca) response to isoproterenol (ISO) were significantly reduced. However, ISO response was reversed by beta2-adrenergic receptor (AR) inhibition. Western blots showed a decrease in beta1-AR and an increase in Ca(v)1.2, beta2-AR, and Galphai3 protein levels. Ca(2+) transient and sarcomere shortening in KO myocytes were unchanged at 1-Hz but reduced at 3-Hz stimulation. Echocardiography in conscious mice revealed an increased basal contractility in KO mice. However, cardiac reserve to work load and beta-adrenergic stimulation was reduced. Surprisingly, KO mice showed a reduced heart rate in response to work load or beta-adrenergic stimulation., Conclusions: Our results implicate physiological CaMKII activity in maintaining normal I(Ca), Ca(2+) handling, excitation-contraction coupling, and the in vivo heart function in response to cardiac stress.

The L-type Ca(2+) channel (LTCC) is the major mediator of Ca(2+) influx in cardiomyocytes, leading to both mechanical contraction and activation of signaling cascades. Among these Ca(2+)-activated cascades is calcineurin, a protein phosphatase that promotes hypertrophic growth of the heart. Coimmunoprecipitations from heart extracts and pulldowns using heterologously expressed proteins provided evidence for direct binding of calcineurin at both the N and C termini of alpha(1)1.2. At the C terminus, calcineurin bound specifically at amino acids 1943 to 1971, adjacent to a well-characterized protein kinase (PK)A/PKC/PKG phospho-acceptor site Ser1928. In vitro assays demonstrated that calcineurin can dephosphorylate alpha(1)1.2. Channel function was increased in voltage-clamp recordings of I(Ca,L) from cultured cardiomyocytes expressing constitutively active calcineurin, consistent with previous observations in cardiac hypertrophy in vivo. Conversely, acute suppression of calcineurin pharmacologically or with specific peptides decreased I(Ca,L). These data reveal direct physical interaction between the LTCC and calcineurin in heart. Furthermore, they demonstrate that calcineurin induces robust increases in I(Ca,L) and highlight calcineurin as a key modulator of pathological electrical remodeling in cardiac hypertrophy.