Influence of gelsolin deficiency on excitation contraction coupling in adult murine cardiomyocytes.

Ion channels involved in cardiac excitation-contraction coupling are linked to the cytoskeleton. Therefore changes in the cytoskeletal actin filaments may influence cardiac membrane currents and electro-mechanical coupling. Depolymerization of actin filaments by gelsolin (gsn) is involved in the organisation of the cytoskeleton by leading to a lower polymerization state. Gsn is activated by Ca(2+) and inhibited by phosphoinositol-bisphosphate (PIP2). Furthermore, gsn has been linked to pathological conditions with reduced contractility like heart failure, amyloidosis and apoptosis. Thus, we hypothesize, that gsn deficiency may change electromechanical properties of freshly isolated ventricular cardiomyocytes. We recorded L-type Ca(2+) current (ICa,L) in whole-cell patch clamp mode in freshly isolated ventricular cardiomyocytes from gsn deficient ((-/-)) and control (gsn(+/+)) mice. Sarcomere shortening was monitored in field-stimulated myocytes from 0.5 Hz to 10 Hz by video microscopy. Shortening-frequency relation, post-rest potentiation and ß-adrenergic stimulation were investigated. ICa,L was increased in gsn(-/-) vs. gsn(+/+) myocytes. Sarcomere shortening amplitude and velocity were enhanced in gsn(-/-) vs. gsn(+/+) at all frequencies. Shortening-frequency relationship showed a biphasic pattern with decay in shortening amplitude between 0.5 and 2 Hz and an increase at higher frequencies in both genotypes. Post-rest characteristics revealed a frequency-dependent decay of post-rest potentiation in gsn(+/+) while it remained stable in gsn(-/-). In gsn(-/-) a reduced response to ß-adrenergic stimulation was observed. Resting sarcomere length was shorter in gsn(-/-) but neither increasing frequency nor ß-adrenergic stimulation induced further decay in any of the genotypes. In summary, gsn deficiency had a profound effect on excitiation-contraction properties and improved systolic function while not affecting diastolic function in unloaded isolated cardiomyocytes. Therefore, gsn mediated effects on contractility may play a role in patients with heart failure and cancer, where gsn levels are known to be elevated.

Echocardiographic assessment of left ventricular mass in neonatal and adult mice: accuracy of different echocardiographic methods.

Echocardiography is an established method to estimate left-ventricular mass (LVM) in mice. Accuracy is determined by cardiac size and morphology and influenced by mathematical models. We investigated accuracy of three common algorithms in three early developmental stages. High-resolution echocardiography was performed in 35 C57/BL6-mice. Therefore, two-dimensional-guided M-mode echocardiography and parasternal short- and long-axis views in B-mode were obtained. LVM was assessed in vivo applying Penn (P), Area Length (AL), and Truncated Ellipsoid (TE) algorithms and validated with histomorphometry. Regression analysis of all mice showed fair estimation of LVM assessed with M-mode-based Penn algorithm (y = 0.6*x - 0.12, r: 0.71). In contrast two-dimensional assessment of LVM revealed close linear relationship with histomorphometry (y(AL)= 1.21*x - 12.1, r: 0.88, y(TE)= 1.38*x - 2.88, r: 0.86). Bias was lowest for LVM-AL at diastole underestimating 3.2%. In concordance with the summarized data, LVM-P revealed lower regression coefficients and significant underestimation in all three subgroups. Small hearts (<50 mg, n = 12) correlated best with LVM-AL at systole. Hearts of adolescent (50-75 mg, n = 13) and adult (75-100 mg, n = 10) mice revealed close linear relationship with LVM-AL and LVM-TE at diastole. Echocardiographic assessment of LVM is feasible in hearts weighting less than 50 mg and can be estimated best in systole. Hearts weighting more than 50 mg are estimated most accurately by means of LVM-AL at diastole.

17 Beta-estradiol regulates nNOS and eNOS activity in the hippocampus.

Estrogen treatment in symptomatic postmenopausal women appears to improve cognitive performance including memory, an effect which may involve enhanced nitric oxide formation in hippocampal neurons. To study whether 17beta-estradiol (E2) affects NO synthase activity in the hippocampus, we investigated the influence of E2 on hippocampal NO synthase expression and activity in female rats. Ovariectomy, which significantly decreased E2 serum levels, reduced neuronal (nNOS) and endothelial NO synthase (eNOS) expression and Ca(2+)-dependent NOS activity. E2 substitution reversed these effects. It is concluded that E2 increases nNOS and eNOS expression and activity in female hippocampus and thus improves hippocampal function.

Increasing myocardial contraction and blood pressure in C57BL/6 mice during early postnatal development.

Knowledge of the developmental changes of cardiovascular parameters in the genetic background of a mouse strain is important for understanding phenotypic changes in transgenic or knockout mouse models for heart disease. We studied arterial blood pressure and myocardial contractility in mice of the common background strain C57BL/6, aged 21 days [postnatal day 21 (P21)] to 580 days. Heart rate increased during maturation from 396 beats/min at P21 to 551 beats/min at postnatal day 50 (P50), and mean arterial blood pressure increased in parallel from 86 to 110 mmHg and remained constant afterward. Echocardiographically determined left ventricular myocardial wall dimensions (R = 0.79, P < 0.0001) and left ventricular mass calculated using the area-length algorithm correlated strongly with histomorphometrical measurements (R = 0.93, P < 0.001). Sarcomere shortening records from isolated ventricular myocytes used as a measure for myocardial contractility revealed a negative shortening-frequency relation under a pacing frequency of 2 Hz and a positive relation above 2 Hz. Shortening amplitudes recorded from P21 myocytes were smaller, and the shortening-frequency relation was less steep than in adult myocytes. A stimulation pause was followed by a negative "staircase" at pacing frequency of < or =6 Hz and a positive staircase at > or =6 Hz. P21 myocytes developed positive staircases at 8 and 10 Hz, and adult myocytes also developed them at 6 Hz. Blood pressure increase during maturation until P50 may originate from increasing single cardiomyocyte contractility.

Effects of cytoskeletal modifications on Ca2+ influx after cerebral ischemia.

The fungal toxin cytochalasin D as well as endogenous gelsolin depolymerize filamentous actin which may induce dynamic uncoupling of membrane ion channels. In vitro application of cytochalasin D reduced NMDA-induced [(3)H]noradrenaline release from mouse brain neocortical slices by 38%. In gsn deficient neocortical synaptosomes [Ca(2+)](i) increase in response to K(+) (30 mM) depolarization was 33% higher than in wild-type. After transient focal cerebral ischemia K(+)-induced [Ca(2+)](i) increase in neocortical synaptosomes was 56% lower than in synaptosomes prepared from the non-ischemic contralateral hemisphere. After in vivo pretreatment with cytochalasin D 10 min before MCA occlusion K(+)-induced [Ca(2+)](i) increase in synaptosomes in vitro prepared 1 h after reperfusion from the ischemic hemisphere was only 25% lower than in contralateral synaptosomes, while cytochalasin D pretreatment in vivo did not reduce K(+)-induced [Ca(2+)](i) increase in vitro. Hence, presynaptic Ca(2+) influx and subsequently neuronal vulnerability are attenuated by increased and are aggravated by decreased F-actin depolymerization.