Role of extracellular and intracellular sources of Ca2+ in sarafotoxin S6b-induced contraction of strips of the rat aorta

Snake Venom Components as Therapeutic Drugs in Ischemic Heart Disease

Ischemic heart disease (IHD), especially myocardial infarction (MI), is a leading cause of death worldwide. Although coronary reperfusion is the most straightforward treatment for limiting the MI size, it has nevertheless been shown to exacerbate ischemic myocardial injury. Therefore, identifying and developing therapeutic strategies to treat IHD is a major medical challenge. Snake venoms contain biologically active proteins and peptides that are of major interest for pharmacological applications in the cardiovascular system (CVS). This has led to their use for the development and design of new drugs, such as the first-in-class angiotensin-converting enzyme inhibitor captopril, developed from a peptide present in Bothrops jararaca snake venom. This review discusses the potential usefulness of snake venom toxins for developing effective treatments against IHD and related diseases such as hypertension and atherosclerosis. It describes their biological effects at the molecular scale, their mechanisms of action according to their different pharmacological properties, as well as their subsequent molecular pathways and therapeutic targets. The molecules reported here have either been approved for human medical use and are currently available on the drug market or are still in the clinical or preclinical developmental stages. The information summarized here may be useful in providing insights into the development of future snake venom-derived drugs.

Cardiovascular Effects of Snake Toxins: Cardiotoxicity and Cardioprotection

Snake venoms, as complex mixtures of peptides and proteins, affect various vital systems of the organism. One of the main targets of the toxic components from snake venoms is the cardiovascular system. Venom proteins and peptides can act in different ways, exhibiting either cardiotoxic or cardioprotective effects. The principal classes of these compounds are cobra cardiotoxins, phospholipases A2, and natriuretic, as well as bradykinin-potentiating peptides. There is another group of proteins capable of enhancing angiogenesis, which include, e.g., vascular endothelial growth factors possessing hypotensive and cardioprotective activities. Venom proteins and peptides exhibiting cardiotropic and vasoactive effects are promising candidates for the design of new drugs capable of preventing or constricting the development of pathological processes in cardiovascular diseases, which are currently the leading cause of death worldwide. For example, a bradykinin-potentiating peptide from Bothrops jararaca snake venom was the first snake venom compound used to create the widely used antihypertensive drugs captopril and enalapril. In this paper, we review the current state of research on snake venom components affecting the cardiovascular system and analyse the mechanisms of physiological action of these toxins and the prospects for their medical application.

The sources of calcium for noradrenaline-induced contraction in the human thoracic internal artery

The aim of the present study was to examine the contribution of intracellular and extracellular calcium sources in contraction caused by noradrenaline (NA) of the human internal thoracic artery (ITA) in vitro. Distal segments of ITA were obtained from 20 patients (aged 38-73, at the time of routine coronary artery surgical revascularization (CABG)). Contractile responses to 10^-6 mol/L NA in the physiological salt solution and in Ca²⁺-free solution without and after incubation with 10^-6 mol/L thapsigargin (TSG) were recorded under isometric conditions. Responses of ITA rings to 1 μM NA without incubation with TSG accounted (% of reaction to 80 mM KCl) 224.70 ± 14.06% in PSS solution, 141.30 ± 8.66% in Ca²⁺-free solution, and 80.03 ± 1.71% after PSS restoration and were statistically significantly different (p < 0.0001, one-way ANOVA). Responses of ITA rings to 1 μM NA with 1 μM TSG accounted (% of reaction to 80 mM KCl) 114.50 ± 2.79% in Ca²⁺-free solution and 36.70 ± 2.38% after PSS restoration. Responses in Ca²⁺-free solution and after PSS restoration without and with TSG were statistically significantly different (p = 0.0257 and p < 0.0001, respectively-t test). ITA contraction is caused by calcium derived not only from the SR and the extracellular matrix. The delivery of calcium to the space surrounding tissue does not immediately deliver calcium to the myofilaments.

Sarafotoxin-induced calcium mobilization in cultured dog tracheal smooth muscle cells

Sarafotoxin b (S6b)-induced changes in intracellular Ca2+ concentration ([Ca2+]i) were monitored in cultured canine tracheal smooth muscle cells (TSMCs) by a fluorescent Ca2+ indicator fura-2. S6b elicited an initial transient peak followed by a sustained elevation of [Ca2+]i. BQ-123, an endothelin-A (ETA) receptor antagonist, had a high affinity to block the rise in [Ca2+]i response to S6b. In the absence of external Ca2+, only an initial transient peak of [Ca2+]i was seen, the sustained elevation of [Ca2+]i could then be evoked by addition of 1.8 mM Ca2+. Ca2+ influx was required for the changes of [Ca2+]i, since the Ca(2+)-channel blockers, diltiazem, verapamil, and Ni2+, decreased both the initial and sustained elevation of [Ca2+]i in response to S6b. TSMCs pretreated with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min attenuated Ca2+ mobilization induced by S6b, which was reversed by staurosporine, a protein kinase C (PKC) inhibitor. The change of [Ca2+]i induced by S6b was attenuated by cholera toxin pretreatment, but not by pertussis toxin. These data demonstrate that the initial detectable increase in [Ca2+]i stimulated by S6b is due to the activation of ETA receptors and subsequent release of Ca2+ from internal stores, whereas the contribution of external Ca2+ follows and partially involves a diltiazem- and verapamil-sensitive process. The inhibition of PMA on S6b-induced Ca2+ mobilization was inversely correlated with membraneous PKC activity.

The receptors for endothelins and their analogues in SK-N-MC neuroblastoma cells

The potency order of peptides to inhibit [125I]endothelin-1 binding and to stimulate phosphatidylinositol phosphate (PtdInsP) turnover in SK-N-MC cells was consistent with the presence of ETA-endothelin receptors. Divalent cations enhanced [125I]endothelin-1 binding by, in the case of Mn2+, increasing radioligand affinity. Mn2+ did not induce conformational changes in endothelin-1, and its effect was maintained in solubilized receptors. Hence, metal ions may directly interact with endothelin receptors. The effects of BQ-123 and [Ala1,3,11,15]endothelin-1 on PtdInsP turnover were investigated. Concentration-response curves of endothelins were modeled by a second-order equation that assumes pseudoirreversible ligand binding.