The Novel Inodilator ORM-3819 Relaxes Isolated Porcine Coronary Arteries: Role of Voltage-Gated Potassium Channel Activation.

Relaxation and changes in the transmembrane potential of vascular smooth muscle induced by ORM-3819, a novel inodilating compound, were investigated in isolated porcine coronary arteries. Isometric tone was studied on arterial rings precontracted by KCl (30 mM), and resting membrane potential was investigated by a conventional microelectrode technique. ORM-3819 in the concentration range 0.38-230.6 µM evoked concentration-dependent relaxation with a maximum value of 58.1% and an effective concentration of the relaxing substance that caused 50% of maximum relaxation of 72.2 µM. The maximum hyperpolarization produced by ORM-3819 at a concentration of 120 µM (-2.6 ± 0.81 mV, N = 10) did not differ significantly from that induced by C-type natriuretic peptide (CNP), an endogenous hyperpolarizing mediator, at a concentration of 1.4 µM (-3.6 ± 0.38 mV, N = 17). The same effect elicited by the known inodilator levosimendan was less pronounced at a concentration of 3.7 µM: -1.82 ± 0.44 mV, N = 22 (P < 0.05 vs. CNP). The voltage-gated potassium channel inhibitor 4-aminopyridine, at a concentration of 5 mM, attenuated the relaxation induced by ORM-3819 at concentrations of 41.6 or 117.2 µM. These results suggest that ORM-3819 is a potent vasodilating agent able to relieve coronary artery vasospasm by causing hyperpolarization of vascular smooth muscle cells through processes involving activation of voltage-gated potassium channels.

VITA-an everyday virtual reality setup for prosthetics and upper-limb rehabilitation.

OBJECTIVE: Currently, there are some 95 000 people in Europe suffering from upper-limb impairment. Rehabilitation should be undertaken right after the impairment occurs and should be regularly performed thereafter. Moreover, the rehabilitation process should be tailored specifically to both patient and impairment. APPROACH: To address this, we have developed a low-cost solution that integrates an off-the-shelf virtual reality (VR) setup with our in-house developed arm/hand intent detection system. The resulting system, called VITA, enables an upper-limb disabled person to interact in a virtual world as if her impaired limb were still functional. VITA provides two specific features that we deem essential: proportionality of force control and interactivity between the user and the intent detection core. The usage of relatively cheap commercial components enables VITA to be used in rehabilitation centers, hospitals, or even at home. The applications of VITA range from rehabilitation of patients with musculodegenerative conditions (e.g. ALS), to treating phantom-limb pain of people with limb-loss and prosthetic training. MAIN RESULTS: We present a multifunctional system for upper-limb rehabilitation in VR. We tested the system using a VR implementation of a standard hand assessment tool, the Box and Block test and performed a user study on this standard test with both intact subjects and a prosthetic user. Furthermore, we present additional applications, showing the versatility of the system. SIGNIFICANCE: The VITA system shows the applicability of a combination of our experience in intent detection with state-of-the art VR system for rehabilitation purposes. With VITA, we have an easily adaptable experimental tool available, which allows us to quickly and realistically simulate all kind of real-world problems and rehabilitation exercises for upper-limb impaired patients. Additionally, other scenarios such as prostheses simulations and control modes can be quickly implemented and tested.

Inotropic effect of NCX inhibition depends on the relative activity of the reverse NCX assessed by a novel inhibitor ORM-10962 on canine ventricular myocytes.

Na+/Ca2+ exchanger (NCX) is the main Ca2+ transporter in cardiac myocytes. Its inhibition could be expected to exert positive inotropic action by accumulation of cytosolic Ca2+ ([Ca2+]i). However, we have observed only a marginal positive inotropic effect upon selective inhibition of NCX, which was enhanced when forward activity was facilitated. Here we attempted to clarify the underlying mechanism of the limited inotropic action of selective NCX inhibition by a novel inhibitor ORM-10962 on canine ventricular myocytes. 1µM ORM-10962 reduced the Ca2+ content of sarcoplasmic reticulum (SR) when the reverse NCX was favoured, while SR Ca2+ content was increased by ORM-10962 under conditions favouring the forward activity, like elevation of [Ca2+]i. L-type Ca2+ current (ICa) was not affected by 1µM ORM-10962 in the absence of SR Ca2+ release, while ICa was suppressed by ORM-10962 during normal Ca2+ cycling. The apparent degree of forward NCX inhibition was dependent on the elevation of [Ca2+]i, suggesting that an increased driving force of forward NCX can also limit the accumulation of [Ca2+i]. We concluded that in healthy myocardium the possible positive inotropic potential of NCX inhibition is considerably weaker than it was expected earlier by theoretical assumptions. The underlying mechanism may involve the autoregulation of Ca2+ handling and/or the preserved inducibility of forward NCX by high [Ca2+]i. This limitation of selective NCX inhibition seen in undiseased myocardium requires further studies in failing heart, which may allow correct evaluation of the potential therapeutic value of selective NCX inhibitors in the treatment of heart failure.

The investigation of the cellular electrophysiological and antiarrhythmic effects of a novel selective sodium-calcium exchanger inhibitor, GYKB-6635, in canine and guinea-pig hearts.

The sodium-calcium exchanger (NCX) is considered as the major transmembrane transport mechanism that controls Ca2+ homeostasis. Its contribution to the cardiac repolarization has not yet been directly studied due to lack of specific inhibitors, so that an urgent need for more selective compounds. In this study, the electrophysiological effects of GYKB-6635, a novel NCX inhibitor, on the NCX, L-type calcium, and main repolarizing potassium currents as well as action potential (AP) parameters were investigated. Ion currents and AP recordings were investigated by applying the whole-cell patch clamp and standard microelectrode techniques in canine heart at 37 °C. Effects of GYKB-6635 were studied in ouabain-induced arrhythmias in isolated guinea-pig hearts. At a concentration of 1 µmol/L, GYKB significantly reduced both the inward and outward NCX currents (57% and 58%, respectively). Even at a high concentration (10 µmol/L), GYKB-6635 did not change the ICaL, the maximum rate of depolarization (dV/dtmax), the main repolarizing K+ currents, and the main AP parameters. GYKB-6635 pre-treatment significantly delayed the time to the development of ventricular fibrillation (by about 18%). It is concluded that GYKB-6635 is a potent and highly selective inhibitor of the cardiac NCX and, in addition, it is suggested to also contribute to the prevention of DAD-based arrhythmias.

Antiarrhythmic potential of drugs targeting the cardiac ryanodine receptor Ca2+ release channel: case study of dantrolene.

Driven by the limitations of the traditional antiarrhythmic pharmacology, current antiarrhythmic research is trying to identify new avenues for the development of specific and safe antiarrhythmic drugs. One of the most promising approaches in this field is the amelioration of the abnormal events in cellular Ca(2+) handling originating from the dysfunction of ryanodine receptor Ca(2+) release complex (RyR), which is an inevitable key factor in the pathology of myocardial dysfunction, remodeling and arrhythmogenesis. Accordingly, both in experimental and clinical situations, inhibition of abnormal activity of RyR, regardless of being the primary cause or a consequence during the pathogenesis appears to exert beneficial effect on disease outcome, including a marked antiarrhythmic defense. Considerable amount of our knowledge in this field originates from studies using dantrolene, a human drug with RyR stabilizing effect. Our review summarizes the cardiovascular pharmacology of dantrolene and the results of its use in experimental models of cardiac diseases, which emphasize a promising perspective for the possible antiarrhythmic application of RyR inhibition in the future.

C-type natriuretic peptide hyperpolarizes and relaxes human penile resistance arteries.

INTRODUCTION: In addition to nitric oxide (NO), it is thought that an endothelium-derived hyperpolarizing factor (EDHF) plays an important role in the relaxation of penile arteries. Recently, it has been shown that C-type natriuretic peptide (CNP) shows the characteristics of EDHF in systemic small arteries. AIM: To investigate the mechanism involved in CNP-evoked vasodilatation and to address whether CNP is an EDHF in human penile resistance arteries. METHODS: Erectile tissue was obtained in connection with transsexual operations. Intracavernous penile resistance arteries were isolated and mounted in microvascular myographs for recording of isometric tension. Membrane potential was recorded by the use of a small glass electrode inserted in the smooth muscle layer. MAIN OUTCOME MEASURE: In vitro evidence for hyperpolarization and vasorelaxation induced by CNP. RESULTS: Acetylcholine (ACh) and CNP hyperpolarized smooth muscle membrane potential in resting penile resistance arteries. In penile small arteries incubated with inhibitors of NO synthase and cyclooxygenase and contracted with phenylephrine, ACh and CNP evoked concentration-dependent relaxations with maximum of 56 +/- 6% and 71 +/- 6%, respectively. Addition of a combination of blockers of small- and intermediate-conductance calcium-activated K(+) channels, apamin plus charybdotoxin, respectively, and a combination thought to block the smooth muscle response of EDHF-type relaxation, barium plus ouabain, markedly reduced ACh- and CNP-evoked relaxation. Iberiotoxin, a blocker of big-conductance calcium-activated K(+) channels inhibited the vasorelaxant responses evoked by ACh and CNP. A selective natriuretic peptide receptor type C (NPR-C) agonist, C-atrial natriuretic factor(4-23) (cANF(4-23)), induced relaxations with less maximum response compared to CNP. CONCLUSION: The present findings suggest that CNP possesses the characteristics of an EDHF in human penile resistance arteries. By activation of natriuretic peptide receptor type B and NPR-C receptors, CNP causes relaxation by activation, respectively, of large-conductance calcium-activated K(+) channels and Na(+)/K(+)-adenosine triphosphatase (ATPase), and barium-sensitive inward rectifier K(+) channels. Modulation of the CNP pathway opens for new treatment modalities of erectile dysfunction.

NEP inhibitors enhance C-type natriuretic peptide-induced relaxation in porcine isolated coronary artery.

C-type natriuretic peptide (CNP), a local regulator of vascular tone and cell proliferation, is eliminated from the circulation via NPR-C receptors and neutral endopeptidase enzyme (NEP, EC. 3.4.24.11). The increased contractility of coronary arteries in different cardiovascular diseases made us study the possible enhancement of vasodilator capacity of exogenously added CNP with concomitant NEP inhibition on porcine coronary arteries in vitro. CNP (0.006-1.4 microM) concentration dependently relaxed the U46619 (0.07-0.4 microM) precontracted preparations in an almost equally effective manner in the presence and absence of functional endothelium with maximum effects of about 40%. The combined NEP/endothelin-converting enzyme inhibitor (NEP/ECE inhibitor), phosphoramidon (10 microM) or the specific inhibitor of the NEP, thiorphan (10 microM) resulted in an enhanced magnitude of CNP-induced relaxation without significant change in the EC50 both on endothelium intact and endothelium deprived preparations. The inhibition of endothelin receptors by PD 142893 (10 microM) enhanced the relaxing effect of CNP in the presence but not in the absence of functional endothelium indicating a functional antagonism between CNP and endothelin. Our results suggest that inhibition of CNP degradation may endue this endogenous peptide with therapeutic potency in cardiovascular diseases.