β 3 -adrenergic receptor (β 3 -AR) activation produces a negative inotropic effect in human ventricles. Here we explored the role of β 3 -AR in the human atrium. Unexpectedly, β 3 -AR activation increased human atrial tissue contractility and stimulated the L-type Ca 2+ channel current (I Ca,L ) in isolated human atrial myocytes (HAMs). Right atrial tissue specimens were obtained from 57 patients undergoing heart surgery for congenital defects, coronary artery diseases, valve replacement, or heart transplantation. The I Ca,L and isometric contraction were recorded using a whole-cell patch-clamp technique and a mechanoelectrical force transducer. Two selective β 3 -AR agonists, SR58611 and BRL37344, and a β 3 -AR partial agonist, CGP12177, stimulated I Ca,L in HAMs with nanomolar potency and a 60%-90% efficacy compared with isoprenaline. The β 3 -AR agonists also increased contractility but with a much lower efficacy (~10%) than isoprenaline. The β 3 -AR antagonist L-748,337, β 1 -/β 2 -AR antagonist nadolol, and β 1 -/β 2 -/β 3 -AR antagonist bupranolol were used to confirm the involvement of β 3 -ARs (and not β 1 -/β 2 -ARs) in these effects. The β 3 -AR effects involved the cAMP/PKA pathway, since the PKA inhibitor H89 blocked I Ca,L stimulation and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) strongly increased the positive inotropic effect. Therefore, unlike in ventricular tissue, β 3 -ARs are positively coupled to L-type Ca 2+ channels and contractility in human atrial tissues through a cAMP-dependent pathway.
Patients with short QT syndrome (SQTS) may present with syncope, ventricular fibrillation or sudden cardiac death. Six SQTS susceptibility genes, encoding cation channels, explain <25% of SQTS cases. Here we identify a missense mutation in the anion exchanger (AE3)-encoding SLC4A3 gene in two unrelated families with SQTS. The mutation causes reduced surface expression of AE3 and reduced membrane bicarbonate transport. Slc4a3 knockdown in zebrafish causes increased cardiac pHi, short QTc, and reduced systolic duration, which is rescued by wildtype but not mutated SLC4A3. Mechanistic analyses suggest that an increase in pHi and decrease in [Cl−]i shortened the action potential duration. However, other mechanisms may also play a role. Altered anion transport represents a mechanism for development of arrhythmia and may provide new therapeutic possibilities.
DNA electrotransfer in vivo for gene therapy is a promising method. For further clinical developments, the efficiency of the method should be increased. It has been shown previously that high efficiency of gene electrotransfer in vivo can be achieved using high-voltage (HV) and low-voltage (LV) pulses. In this study we evaluated whether HV and LV pulses could be optimized in vitro for efficient DNA electrotransfer. Experiments were performed using Chinese hamster ovary (CHO) cells. To evaluate the efficiency of DNA electrotransfer, two different plasmids coding for GFP and luciferase were used. For DNA electrotransfer experiments 50 microl of CHO cell suspension containing 100, 10 or 1 microg/ml of the plasmid were placed between plate electrodes and subjected to various combinations of HV and LV pulses. The results showed that at 100 microg/ml plasmid concentration LV pulse delivered after HV pulse increased neither the percentage of transfected cells nor the total transfection efficiency (luciferase activity). The contribution of the LV pulse was evident only at reduced concentration (10 and 1 microg/ml) of the plasmid. In comparison to HV (1,200 V/cm, 100 micros) pulse, addition of LV (100 V/cm, 100 ms) pulse increased transfection efficiency severalfold at 10 microg/ml and fivefold at 1 microg/ml. At 10 microg/ml concentration of plasmid, application of four LV pulses after HV pulse increased transfection efficiency by almost 10-fold. Thus, these results show that contribution of electrophoretic forces to DNA electrotransfer can be investigated in vitro using HV and LV pulses.
So far, the optical mapping of cardiac electrical signals using voltage-sensitive fluorescent dyes has only been performed in experimental studies because these dyes are not yet approved for clinical use. It was recently reported that the well-known and widely used fluorescent dye indocyanine green (ICG), which has FDA approval, exhibits voltage sensitivity in various tissues, thus raising hopes that electrical activity could be optically mapped in the clinic. The aim of this study was to explore the possibility of using ICG to monitor cardiac electrical activity. Optical mapping experiments were performed on Langendorff rabbit hearts stained with ICG and perfused with electromechanical uncouplers. The residual contraction force and electrical action potentials were recorded simultaneously. Our research confirms that ICG is a voltage-sensitive dye with a dual-component (fast and slow) response to membrane potential changes. The fast component of the optical signal (OS) can have opposite polarities in different parts of the fluorescence spectrum. In contrast, the polarity of the slow component remains the same throughout the entire spectrum. Separating the OS into these components revealed two different voltage-sensitivity mechanisms for ICG. The fast component of the OS appears to be electrochromic in nature, whereas the slow component may arise from the redistribution of the dye molecules within or around the membrane. Both components quite accurately track the time of electrical signal propagation, but only the fast component is suitable for estimating the shape and duration of action potentials. Because ICG has voltage-sensitive properties in the entire heart, we suggest that it can be used to monitor cardiac electrical behavior in the clinic.
This review analyzes the structure and regulation mechanisms of voltagedependent L-type Ca2+ channel in the heart. L-type Ca2+ channels in the heart are composed of four different polypeptide subunits, and the pore-forming subunit a1 is the most important part of the channel. In cardiac myocytes, Ca2+ enter cell cytoplasm from extracellular space mainly through L-type Ca2+ channels; these channels are very important system in heart Ca2+ uptake regulation. L-type Ca2+ channels are responsible for the activation of sarcoplasmic reticulum Ca2+ channels (RyR2) and force of muscle contraction generation in heart; hence, activity of the heart depends on L-type Ca2+ channels. Phosphorylation of channel-forming subunits by different kinases is one of the most important ways to change the activity of L-type Ca2+ channel. Additionally, the activity of L-type Ca2+ channels depends on Ca2+ concentration in cytoplasm. Ca2+ current in cardiac cells can facilitate, and this process is regulated by phosphorylation of L-type Ca2+ channels and intracellular Ca2+ concentration. Disturbances in cellular Ca2+ transport and regulation of L-type Ca2+ channels are directly related to heart diseases, life quality, and life span.
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