Single acute stress-induced progesterone and ovariectomy alter cardiomyocyte contractile function in female rats

Aim To assess how ovarian-derived sex hormones (in particular progesterone) modify the effects of single acute stress on the mechanical and biochemical properties of left ventricular cardiomyocytes in the rat. Methods Non-ovariectomized (control, n = 8) and ovariectomized (OVX, n = 8) female rats were kept under normal conditions or were exposed to stress (control-S, n = 8 and OVX-S, n = 8). Serum progesterone levels were measured using a chemiluminescent immunoassay. Left ventricular myocardial samples were used for isometric force measurements and protein analysis. Ca2+-dependent active force (Factive), Ca2+-independent passive force (Fpassive), and Ca2+-sensitivity of force production were determined in single, mechanically isolated, permeabilized cardiomyocytes. Stress- and ovariectomy-induced alterations in myofilament proteins (myosin-binding protein C [MyBP-C], troponin I [TnI], and titin) were analyzed by sodium dodecyl sulfate gel electrophoresis using protein and phosphoprotein stainings. Results Serum progesterone levels were significantly increased in stressed rats (control-S, 35.6 ± 4.8 ng/mL and OVX-S, 21.9 ± 4.0 ng/mL) compared to control (10 ± 2.9 ng/mL) and OVX (2.8 ± 0.5 ng/mL) groups. Factive was higher in the OVX groups (OVX, 25.9 ± 3.4 kN/m2 and OVX-S, 26.3 ± 3.0 kN/m2) than in control groups (control, 16.4 ± 1.2 kN/m2 and control-S, 14.4 ± 0.9 kN/m2). Regarding the potential molecular mechanisms, Factive correlated with MyBP-C phosphorylation, while myofilament Ca2+-sensitivity inversely correlated with serum progesterone levels when the mean values were plotted for all animal groups. Fpassive was unaffected by any treatment. Conclusion Stress increases ovary-independent synthesis and release of progesterone, which may regulate Ca2+-sensitivity of force production in left ventricular cardiomyocytes. Stress and female hormones differently alter Ca2+- dependent cardiomyocyte contractile force production, which may have pathophysiological importance during stress conditions affecting postmenopausal women

Cell-to-cell variability in troponin I phosphorylation in a porcine model of pacing-induced heart failure

We tested the hypothesis that myocardial contractile protein phosphorylation and the Ca2+ sensitivity of force production are dysregulated in a porcine model of pacing-induced heart failure (HF). The level of protein kinase A (PKA)-dependent cardiac troponin I (TnI) phosphorylation was lower in the myocardium surrounding the pacing electrode (pacing site) of the failing left ventricle (LV) than in the controls. Immunohistochemical assays of the LV pacing site pointed to isolated clusters of cardiomyocytes exhibiting a reduced level of phosphorylated TnI. Flow cytometry on isolated and permeabilized cardiomyocytes revealed a significantly larger cell-to-cell variation in the level of TnI phosphorylation of the LV pacing site than in the opposite region in HF or in either region in the controls: the interquartile range (IQR) on the distribution histogram of relative TnI phosphorylation was wider at the pacing site (IQR = 0.53) than that at the remote site of HF (IQR = 0.42; P = 0.0047) or that of the free wall of the control animals (IQR = 0.36; P = 0.0093). Additionally, the Ca2+ sensitivities of isometric force production were higher and appeared to be more variable in single permeabilized cardiomyocytes from the HF pacing site than in the healthy myocardium. In conclusion, the level of PKA-dependent TnI phosphorylation and the Ca2+ sensitivity of force production exhibited a high cell-to-cell variability at the LV pacing site, possibly explaining the abnormalities of the regional myocardial contractile function in a porcine model of pacing-induced HF

Hearts of surviving MLP-KO mice show transient changes of intracellular calcium handling

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Effects of neonatal capsaicin desensitization on sensory TRPV1 expression.

<p>TRPV1 expression was examined in the dorsal root ganglia of control and capsaicin desensitized (neonatal capsaicin treatment) adult rats. Tissue sections were probed with antibodies specific to TRPV1 (red) and neurofilament (green). TRPV1 expression was present in a subset of sensory neurons in control rats, which was missing in desensitized rats within the dorsal root ganglia. However, TRPV1 immunoreactivity was also found in non-neuronal cell types, located at the outer regions of ganglia (regions occupied by sensory neurons are indicated by the freehand drawing). Images are representative of at least 10 sections.</p

Functional effects of acute capsaicin desensitization on vascular TRPV1.

<p>The short-term effects of capsaicin were tested here. Arterioles were isolated from control rats and were treated with capsaicin (1 µM, First treatment). Capsaicin was washed away after the 20 min long treatment and the arterioles were incubated in the physiological buffer alone for 40 min (regeneration). Then capsaicin effects we re-tested (Second treatment) to estimate the level of tachyphylaxis (n = 6 arteries were tested, symbols represent the mean ± SEM of time-matched arteriolar diameter). Acute desensitization to capsaicin was apparent upon the first treatment (decrease and then increase in arteriolar diameter in the continuous presence of capsaicin, maximal decrease was 70±3% at 95 s after capsaicin application, Panel A). The magnitude of the response was decreased upon the second capsaicin treatment on the same arterioles (tachyphylaxis, decreased response to repeated capsaicin stimuli, maximal decrease was 27±9% at 125 s after capsaicin application, Panel A). This acute capsaicin desensitization (20 min treatment) did not affect norepinephrine mediated constrictions (symbols represent the mean ± SEM of n = 6 determinations, Panel B) or acetylcholine mediated dilations (symbols represent the mean ± SEM, n = 6, Panel C).</p

Effects of neonatal capsaicin desensitization on sensory functions.

<p>Rats were treated with saline (Control) or with capsaicin (Desensitized) at 14 days of life. Sensory functions were measured 10 weeks after capsaicin treatment. (A) Eye wiping (a measure of capsaicin evoked sensory irritation) was reduced in desensitized rats (n = 10 in both groups, p<0.001). (B) Plasma extravasation was similarly reduced (Evans blue accumulation, a measure of capsaicin mediated neurogenic inflammation) (n = 9 for Control and n = 5 for Desensitized, p = 0.03).</p

Effects of neonatal capsaicin desensitization on vascular TRPV1 expression.

<p>Skeletal muscle (gracilis muscle of the rat) tissue sections were stained with anti-TRPV1 (red) and anti-vascular smooth muscle actin (SMA, green) antibodies. There appeared a complete overlap of the staining patterns (merged images). Arteriolar TRPV1 expression was not affected by neonatal capsaicin desensitization, similarly to the vascular TRPV1 in the dorsal root ganglia. Images are representative of at least 10 sections.</p