Bioelectromagnetics29:549^558(2008) ExogenousHydrogenPeroxideasaPossible MessengerfortheStimulationEffectof MagnetizedPhysiologicalSolution onHeartContractility GayaneAyrapetyan,ErnaDadasyan,HovikHayrapetyan,andSinerikAyrapetyan* UNESCO Chair-Life Sciences International Postgraduate Educational Center, Yerevan, Armenia The dual effect of magnetized physiological solution (MPS) on snail heart muscle contractility (muscle relaxation and stimulation of heartbeat) was shown previously. The MPS-induced relaxation of the heart muscle has been explained by activation of cGMP-dependent Ca 2þ effluxes from the muscle; however, the mechanism of the stimulating effect of MPS on heartbeat remains unclear. As in the presence of paramagnetic oxygen molecules, magnetic fields could generate the exogenous reactive oxygen species such as hydrogen peroxide (H 2 O 2 ), we hypothesize that H 2 O 2 may play a role as the possible messengers through which the activation effect of MPS on heartbeat is realized. To test this hypothesis, the dose-dependent effects of exogenous H 2 O 2 on heart muscle contractility and 45 Ca uptake were studied. Here we compared the obtained data with the previous results of the effects of MPS on heart muscle contractility and 45 Ca uptake. We found that exogenous H 2 O 2 and MPS have similar effects on Na þ –K þ pump-induced transient inhibition of muscle contractility and 45 Ca uptake. The Na þ –K þ pump-induced depression of H 2 O 2 -sensitivity of muscle contractility is determined by activation of Ca 2þ efflux from the cell. On the basis of these data we suggest the exogenous H 2 O 2 as a possible messenger through which the stimulation effect of MPS on heart muscle is realized. Bioelectromagnetics 29:549–558, 2008. ß 2008 Wiley-Liss, Inc. Key words: snail heart muscle; contractility; magnetized physiological solution; reactive oxygen species; exogenous H 2 O 2 ; 45 Ca uptake; Na þ –K þ pump INTRODUCTION Earlier it was shown that metabolic regulation of the cell volume and the effective surface of cell membrane is a powerful mechanism underlying the metabolic regulation of a number of functionally active protein molecules in the membrane, which have enzymatic, channel forming and receptor properties [Ayrapetyan, 1980; Ayrapetyan et al., 1985]. It was also shown that 15–30-min exposure to the 0.2 T static magnetic field (SMF) caused dehydration of the tissue and cells, and decreased number of ouabain binding sides (pump units) and acetylcholine receptors in the membrane, in in vivo and in vitro experiments [Danielyan and Ayrapetyan, 1999; Danielyan et al., 1999; Ayrapetyan et al., 2004]. The SMF-induced de- hydration has been explained by activation of electro- genic Na þ –K þ pump, and as a result, decreased intracellular Ca 2þ by cGMP-dependent Ca 2þ efflux. The dual effect of magnetized physiological solution (MPS) on snail heart muscle contractility (muscle relaxation and stimulation of heartbeat) was shown previously [Ayrapetyan et al., 2005]. The relaxing effect of MPS on heart muscle was explained by a decrease of CO 2 solubility in cell bathing medium [Akopian and Ayrapetyan, 2005], leading to a decrease of intracellular Ca ions as a result of activation of cGMP-dependant Ca 2þ efflux [Ayrapetyan et al., 2005]. However, the stimulatory mechanism of MPS effect on heartbeat is not yet clear. ß 2008Wiley-Liss,Inc. —————— Grant sponsor: Armenian Ministry of Education and Science; Grant number: 0595; Grant sponsor: National Foundation of Science and Advanced Technologies (NFSAT); Grant number: GRSP 36/06. *Correspondence to: Sinerik Ayrapetyan, UNESCO Chair-Life Sciences International Postgraduate Educational Center, 31 Acharyan St., 0040 Yerevan, Armenia. E-mail: info@biophys.am Received for review 21 March 2007; Final revision received 26 February 2008 DOI 10.1002/bem.20421 Published online 1 May 2008 in Wiley InterScience (www.interscience.wiley.com).