Impact of quetiapine on ion channels and contractile dynamics in rat ventricular myocyte.

Antipsychotic drugs often lead to adverse effects, including those related to the cardiovascular system. Of these, quetiapine is known to cause significant changes in the QT interval although the underlying mechanism remains mysterious, prompting us to examine its effects on cardiac electrophysiological properties. Therefore, we investigated the effect of quetiapine on contraction, action potential (AP), and the associated membrane currents such as L-type Ca2+ and K+ using the whole-cell patch clamp method to examine its impacts on isolated rat ventricular myocytes. Our results showed that (1) quetiapine reduces cell contractility in a concentration-dependent manner and (2) leads to a significant prolongation in the duration of AP in isolated ventricular myocytes. This effect was both concentration and frequency-dependent; (3) quetiapine significantly decreased the Ca2+, transient outward K+, and steady-state K+ currents. However, only high concentration of quetiapine (100 µM) could significantly change the activation and reactivation kinetics of L-type Ca2+ channels. This study demonstrates that QT extension induced by quetiapine is mainly associated with the prolongation of AP. Moreover, quetiapine caused a significant decrease in contractile force and excitability of ventricular myocytes by suppressing Ca2+ and K+ currents.

Investigation of Cyclo-Z Therapeutic Effect on Insulin Pathway in Alzheimer's Rat Model: Biochemical and Electrophysiological Parameters.

Cyclo (his-pro-CHP) plus zinc (Zn+2) (Cyclo-Z) is the only known chemical that increases the production of insulin-degrading enzyme (IDE) and decreases the number of inactive insulin fragments in cells. The aim of the present study was to systematically characterize the effects of Cyclo-Z on the insulin pathway, memory functions, and brain oscillations in the Alzheimer's disease (AD) rat model. The rat model of AD was established by bilateral injection of Aß42 oligomer (2,5nmol/10µl) into the lateral ventricles. Cyclo-Z (10mg Zn+2/kg and 0.2mg CHP/kg) gavage treatment started seven days after Aß injection and lasted for 21 days. At the end of the experimental period, memory tests and electrophysiological recordings were performed, which were followed by the biochemical analysis. Aß42 oligomers led to a significant increase in fasting blood glucose, serum insulin, Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and phospho-tau-Ser356 levels. Moreover, Aß42 oligomers caused a significant decrement in body weight, hippocampal insulin, brain insulin receptor substrate (IRS-Ser612), and glycogen synthase kinase-3 beta (GSK-3ß) levels. Also, Aß42 oligomers resulted in a significant reduction in memory. The Cyclo-Z treatment prevented the observed alterations in the ADZ group except for phospho-tau levels and attenuated the increased Aß42 oligomer levels in the ADZ group. We also found that the Aß42 oligomer decreased the left temporal spindle and delta power during ketamine anesthesia. Cyclo-Z treatment reversed the Aß42 oligomer-related alterations in the left temporal spindle power. Cyclo-Z prevents Aß oligomer-induced changes in the insulin pathway and amyloid toxicity, and may contribute to the improvement of memory deficits and neural network dynamics in this rat model.

Pharmacological blockade of angiotensin II receptor restores diabetes-associated reduction of store operated Ca2+ entry in adult cardiomyocytes.

The store-operated Ca2+ entry (SOCE) represents an important route for generating cellular Ca2+ signals that are implicated in physiological and various pathological scenarios that include diabetic cardiomyopathy (DM-CMP) which is well known to have Ca2+ dysregulation among other salient features. In this study, we investigated the role of SOCE in Ca2+ handling of cardiomyocytes obtained from adult male Wistar rats that were made diabetic by intraperitoneal administration of streptozotocin (STZ 50 mg/kg). We also included another group of rats with diabetes induced by STZ administration but received an angiotensin II receptor blocker - losartan. In whole cell recordings with isolated cardiomyocytes, the SOCE-representative whole-cell current ICRAC was found to be significantly reduced for the diabetic group compared to the control group and chronic losartan treatment could restore ICRAC to a level comparable to the control group. However, in contrast to the observed reduction in ICRAC, Orai1 and Orai3 proteins were found to be significantly upregulated in diabetic condition whereas no significant change in the expression levels of Stim1, Stim2 and Orai2 was observed. Also, losartan treatment did not affect the expression pattern of these key proteins for SOCE in diabetic group. The observed imbalance between the functional read out of SOCE (peak ICRAC size) and expression levels of the underlying proteins was puzzling but could be, among other possibilities, due to impairment of interaction between Stim and Orai proteins. We argue that the observed changes in SOCE with diabetes could be a contributing factor for the Ca2+ dyshomeostasis associated with diabetic cardiomyopathies and blockade of angiotensin II receptor may potentially restore normal SOCE in diabetic cardiomyocytes.

Ellagic Acid Prevents Ca2+ Dysregulation and Improves Functional Abnormalities of Ventricular Myocytes via Attenuation of Oxidative Stress in Pathological Cardiac Hypertrophy.

The aim of this study was to investigate whether ellagic acid (EA) treatment can prevent changes in contractile function and Ca2+ regulation of cardiomyocytes in pathologic cardiac hypertrophy. Groups were assigned as Con group; an ISO group in which the rats received isoproterenol alone (5 mg/kg/day); and an ISO + EA group in which the rats received isoproterenol and EA (20 mg/kg/day) for 4 weeks. Subsequently, fractional shortening, intracellular Ca2+ signals, and L-type Ca2+ currents of isolated ventricular myocytes were recorded. Protein expression levels were also determined by the Western blotting method. The survival rate was increased, and the upregulated cardiac hypertrophy markers were significantly attenuated with the EA treatment. The fractional shortening and relaxation rate of myocytes was decreased in the ISO group, whereas EA significantly improved these changes. Ventricular myocytes of the ISO + EA rats displayed lower diastolic Ca2+ levels, higher Ca2+ transients, shorter Ca2+ decay, and higher L-type Ca2+ currents than those of ISO rats. Protein expression analyses indicated that the upregulated p-PLB and p-CaMKII expressions were restored by EA treatment, suggesting improved calcium handling in the ISO + EA rat heart. Moreover, ISO rats displayed significantly increased expression of p-22phox and p47phox subunits of NOX2 protein. Expression of the p22phox subunit was reduced with EA administration, while the decrease in p47phox did not reach a significant level. The increased ROS impairs Ca2+ homeostasis and contractile activity of cardiac myocytes, whereas chronic EA administration prevents Ca2+ dysregulation and functional abnormalities associated with pathological cardiac hypertrophy via the diminution of oxidative stress.

Rosuvastatin Reduces L-Type Ca2+ Current and Alters Contractile Function in Cardiac Myocytes via Modulation of ß-Adrenergic Receptor Signaling.

Rosuvastatin is one of the most used statins to lower plasma cholesterol levels. Although previous studies have reported remarkable cardiovascular effects of rosuvastatin (RSV), the mechanisms of these effects are largely unknown. In this study, we investigated the acute effects of RSV on L-type Ca2+ currents and contractile function of ventricular myocytes under basal conditions and during ß-adrenergic stimulation. The effects of RSV were investigated in freshly isolated adult rat ventricular myocytes. L-type Ca+2 currents and myocyte contractility were recorded using patch-clamp amplifier and sarcomere length detection system. All experimental recordings were performed at 36 ± 1 °C. L-type Ca+2 currents were significantly reduced with the administration of 1 µM RSV (~ 24%) and this reduction in Ca2+ currents was observed at almost all potential ranges applied. Suppression of L-type Ca2+ current by RSV was prevented by adenylyl cyclase (AC) and protein kinase A (PKA) inhibitors SQ 22536 and KT5720, respectively. However, inhibition of Rho-associated kinases (ROCKs) by Y-27632 or nitric oxide synthase (NOS) by L-NAME failed to circumvent the inhibitory effect of RSV. Finally, we examined the effect of RSV during ß-adrenergic receptor stimulation by isoproterenol and observed that RSV significantly suppresses the ß-adrenergic responses in both L-type Ca2+ currents and contraction parameters. In conclusion, RSV modulates the ß-adrenergic signaling cascade and thereby mimics the impact of ß-adrenergic receptor blockers in adult ventricular myocytes through modulation of the AC-cAMP-PKA pathway.