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      Vasoconstrictor effect of Africanized honeybee ( Apis mellifera L.) venom on rat aorta

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          Abstract

          Background

          Apis mellifera stings are a problem for public health worldwide, particularly in Latin America due to the aggressiveness of its Africanized honeybees. Massive poisoning by A. mellifera venom (AmV) affects mainly the cardiovascular system, and several works have described its actions on heart muscle. Nevertheless, no work on the pharmacological action mechanisms of the AmV in isolated aorta has been reported. Thus, the present work aimed to investigate the actions of AmV and its main fractions, phospholipase A 2 (PLA 2) and melittin, on isolated aorta rings and a probable action mechanism.

          Results

          AmV and the complex PLA 2 + melittin (0.1-50 μg/mL) caused contraction in endothelium-containing aorta rings, but neither isolated PLA 2 nor melittin were able to reproduce the effect. Endothelium removal did not change the maximum vasoconstrictor effect elicited by AmV. Ca 2+-free medium, as well as treatment with phentolamine (5 μM), verapamil (10 μM), losartan (100 μM), and U-73122 (10 μM, a phospholipase C inhibitor), eliminated the AmV-induced contractile effects.

          Conclusions

          In conclusion, AmV caused contractile effect in aorta rings probably through the involvement of voltage-operated calcium channels, AT1 and α-adrenergic receptors via the downstream activation of phospholipase C. The protein complex, PLA 2 + melittin, was also able to induce vasoconstriction, whereas the isolated proteins were not.

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          Most cited references29

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          The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine.

          Robert F. Furchgott, John Zawadzki (1980)
          Despite its very potent vasodilating action in vivo, acetylcholine (ACh) does not always produce relaxation of isolated preparations of blood vessels in vitro. For example, in the helical strip of the rabbit descending thoracic aorta, the only reported response to ACh has been graded contractions, occurring at concentrations above 0.1 muM and mediated by muscarinic receptors. Recently, we observed that in a ring preparation from the rabbit thoracic aorta, ACh produced marked relaxation at concentrations lower than those required to produce contraction (confirming an earlier report by Jelliffe). In investigating this apparent discrepancy, we discovered that the loss of relaxation of ACh in the case of the strip was the result of unintentional rubbing of its intimal surface against foreign surfaces during its preparation. If care was taken to avoid rubbing of the intimal surface during preparation, the tissue, whether ring, transverse strip or helical strip, always exhibited relaxation to ACh, and the possibility was considered that rubbing of the intimal surface had removed endothelial cells. We demonstrate here that relaxation of isolated preparations of rabbit thoracic aorta and other blood vessels by ACh requires the presence of endothelial cells, and that ACh, acting on muscarinic receptors of these cells, stimulates release of a substance(s) that causes relaxation of the vascular smooth muscle. We propose that this may be one of the principal mechanisms for ACh-induced vasodilation in vivo. Preliminary reports on some aspects of the work have been reported elsewhere.
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            Smooth muscle contraction and relaxation.

            R Clinton Webb (2003)
            This brief review serves as a refresher on smooth muscle physiology for those educators who teach in medical and graduate courses of physiology. Additionally, those professionals who are in need of an update on smooth muscle physiology may find this review to be useful. Smooth muscle lacks the striations characteristic of cardiac and skeletal muscle. Layers of smooth muscle cells line the walls of various organs and tubes in the body, and the contractile function of smooth muscle is not under voluntary control. Contractile activity in smooth muscle is initiated by a Ca(2+)-calmodulin interaction to stimulate phosphorylation of the light chain of myosin. Ca(2+) sensitization of the contractile proteins is signaled by the RhoA/Rho kinase pathway to inhibit the dephosphorylation of the light chain by myosin phosphatase, thereby maintaining force generation. Removal of Ca(2+) from the cytosol and stimulation of myosin phosphatase initiate the process of smooth muscle relaxation.
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              Ion channels and vascular tone.

              Hartland Jackson (1999)
              Ion channels in the plasma membrane of vascular muscle cells that form the walls of resistance arteries and arterioles play a central role in the regulation of vascular tone. Current evidence indicates that vascular smooth muscle cells express at least 4 different types of K(+) channels, 1 to 2 types of voltage-gated Ca(2+) channels, >/=2 types of Cl(-) channels, store-operated Ca(+) (SOC) channels, and stretch-activated cation (SAC) channels in their plasma membranes, all of which may be involved in the regulation of vascular tone. Calcium influx through voltage-gated Ca(2+), SOC, and SAC channels provides a major source of activator Ca(2+) used by resistance arteries and arterioles. In addition, K(+) and Cl(-) channels and the Ca(2+) channels mentioned previously all are involved in the determination of the membrane potential of these cells. Membrane potential is a key variable that not only regulates Ca(+2) influx through voltage-gated Ca(2+) channels, but also influences release of Ca(2+) from internal stores and Ca(2+)- sensitivity of the contractile apparatus. By controlling Ca(2+) delivery and membrane potential, ion channels are involved in all aspects of the generation and regulation of vascular tone.
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                Author and article information

                Contributors
                Paulo César P Sousa
                Teresinha S Brito
                Daniel S Freire
                Rafael M Ximenes
                Pedro Jorge C Magalhães
                Helena SA Monteiro
                Renata S Alves
                Alice Maria C Martins
                Daniela O Toyama
                Marcos H Toyama
                Journal
                Journal ID (nlm-ta): J Venom Anim Toxins Incl Trop Dis
                Journal ID (iso-abbrev): J Venom Anim Toxins Incl Trop Dis
                Title: The Journal of Venomous Animals and Toxins Including Tropical Diseases
                Publisher: BioMed Central
                ISSN (Electronic): 1678-9199
                Publication date Collection: 2013
                Publication date (Electronic): 25 September 2013
                Volume: 19
                Page: 24
                Affiliations
                [1 ]Department of Physiology and Pharmacology, Federal University of Ceará, Fortaleza, Ceará State, Brazil
                [2 ]Department of Clinical and Toxicological Analyses, Federal University of Ceará, Fortaleza, Ceará State, Brazil
                [3 ]Center of Biological and Health Sciences, Mackenzie Presbyterian University, São Paulo, São Paulo State, Brazil
                [4 ]Paulista Coast Experimental Campus, São Paulo State University (UNESP – Univ Estadual Paulista), São Vicente, São Paulo State, Brazil
                [5 ]Department of Antibiotics, Federal University of Pernambuco, Recife, Pernambuco State, Brazil
                Article
                Publisher ID: 1678-9199-19-24
                DOI: 10.1186/1678-9199-19-24
                PMC ID: 3849866
                PubMed ID: 24066982
                SO-VID: 1dec852a-17f5-4f8c-8501-9e1220536f51
                Copyright © Copyright © 2013 Sousa et al.; licensee BioMed Central Ltd.
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 6 April 2013
                Date accepted : 3 September 2013
                Categories
                Subject: Research

                Keywords: apis mellifera,venom,mellitin,phospholipase a2,aorta
                Data availability:
                Keywords: apis mellifera, venom, mellitin, phospholipase a2, aorta

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