The Effect Of Silver Nanoparticles And Low Potassium On The Transmembrane Potential Of Ventricular Myocytes

Background and objective Silver nanoparticles(Ag-NPs)is one of the most widely used nanomaterials in many fields.Except for their excellent common characteristics,Ag-NPs also have broad-spectrum and highly effective anti-bacteria effects and wound healing-promoting effects.Therefore,Ag-NPs are widely applicated not only in the field of electricity,but also in water sterilization,antibacterial medical devices,wound dressings,food preservation,cosmetics and tracking of biomolecules.Along with the extensive application of the Ag-NPs,the probability and risk for organisms and human beings to contact or ingest Ag-NPs increase,and therefore attention has been raised over the biosafety of Ag-NPs.Many studies show that Ag-NPs has cytotoxic effect.At present,studies have proved that the Ag-NPs are toxic to liver,lung and nervous system.However,cardiotoxic effect of Ag-NPs is still rarely reported.This work aims to investigate the effect of Ag-NPs on the transmembrane potentials(TMP)of cardiomyocytes.Materials and Methods Isolated left ventricular papillary muscles of C57BL/6J mice were used as a model.Standard glass microelectrode technique was applied to intracellularly record the transmembrane potentials of cardiomyocytes of the papillary muscles.Changes in various parameters of the resting potential(RP)and action potential(AP)after Ag-NPs application were analyzed.Results The shape of TMP began to change 8-15 min after adding Ag-NPs to the tissue chamber(Ag-NPs final concentration 10 ?g/ml).The resting potential(RP)was decreased(depolarizing),the action potential amplitude(APA)and the maximum depolarization velocity(Vmax-dep)were gradually reduced by Ag-NPs.About 30-80 min after Ag-NPs application,the threshold intensity for generating APs increased,reflecting a reduction of cell excitability.In addition,the action potentials showed a smaller and abnormal morphology.Quantitative statistics of the transmembrane potential changes are as follows.(1)Changes in RP:before Ag-NPs,the normal control RP value was-67.16±1.37 mV(n=5).After adding Ag-NPs to the chamber,RPs gradually decreased and reached a stabilizing,smaller value-38.44± 2.20 mV(n=5)(P<0.0001 vs.control).(2)Changes in APA and Vmax-dep:normal control APA was 84.8 ± 2.03 mV(n=5).APA and Vmax-dep gradually decreased after Ag-NPs application,APA was reduced finally to 31.13± 2.43 mV and 30%-40%of the control value;Vmax-dep was reduced to 10.99 ± 2.04 V/sec and about 10%of the control value.(3)Changes in action potential duration(APD):the normal control values of APDio,APD20,APD50 and APD90 were respectively 1.9 ± 0.44 ms,4.14 ± 0.92 ms,12.32±1.47 ms and 72.56 ± 6.51 ms.After application of Ag-NPs and at the time when APA was decreased to 40%of the control APA value,APD10 was prolonged to 3.63 ± 0.65 ms(P<0.05 vs.control,n=5),APD20 was prolonged to 5.97 ± 0.98 ms(P<0.05 vs.control,n=5);APD50 prolonged to 18.3 ± 1.94 ms(P=0.0506,n=5);APD90 prolonged to 108.6±10.57 ms(P<0.05 vs.control,n=5).Conclusions Ag-NPs at 10 ?g/ml exert significant effects on the transmembrane potentials of mice ventricular myocytes.Ag-NPs decrease the RP(depolarizing),reduce the APA and Vmax-dep,but increase the threshold intensity and delay the repolarization process.The impacts of Ag-NPs may potentially decrease the excitability and conductivity of cardiac muscle and trigger arrhythmia in vivo.These "toxic" effects of Ag-NPs on cardiomyocytes should be noticed in future study and clinical practice.Background and objective Hypokalemia is a clinical complication or pathophysiological status in many diseases,and has a significant impact on the electrophysiological activity of excitable cells,and can cause serious events such as fatal arrhythmia,skeletal muscle paralysis.Currently,there still are some ambiguity and lack of detailed quantitative study over the impacts of hypokalemia on the electrophysiology of cardiomyocytes.The present study was designed to investigate the effects of hypokalemia with different K+concentrations and different treatment times on the transmembrane potentials of cardiomyocytes,aiming to clarify the detailed effects of hypokalemia on myocardial electrophysiology.Materials and methods Isolated left ventricular papillary muscle of C57BL/6J mice were used as a model.The transmembrane potentials of the muscle cells were recorded intracellularly using the standard microelectrode technique.Different-degree hypokalemia were mimicked by Tyrode's solution containing different concentrations of K+which perfused the muscle strips.The K+concentrations(in mM)were set as:normal(control)potassium 5.4,moderate hypokalemia 3,severe hypokalemia 2 or 1,and extreme hypokalemia 0.Resting potential(RP),depolarization and repolarization of action potential(AP),after-depolarization,triggered activity and excitability were recorded and analyzed,with a special notice on the dose-response and time-response relationships in the study.Results(1)Hypokalemia showed bidirectional effects on the RP:moderate hypokalemia increased the RP(i.e.,hyperpolarization),while severe and extreme hypokalemia first increased and then decreased the RP,and the RP gradually stabilized at a smaller level.(2)Effects of hypokalemia on the depolarization of AP:moderate hypokalemia increased the action potential amplitude(APA)due to increased RP but not an increase of the overshot;severe hypokalemia(K+2 mM)dramatically decreased the APA and maximal depolarization velocity(Vmax-dep),and the AP shape became a"pygmy" type configuration.Longer treatment with severe and extreme hypokalemia(K+1 mM or 0 mM)led to loss of cell excitability and AP could not be induced by electrical stimulus.(3)Effects of hypokalemia on the repolarization of AP:moderate hypokalemia shortened the action potential duration(APD)at APD10,APD20,APD50 and APD90,but prolonged the total APD mainly due to a longer APD tail(APD90-APD100),and increase the maximal repolarization velocity(Vmax-rep).(4)Hypokalemia increased the incidence probabilities of spontaneous AP,after-depolarization and triggered activity,if compared with cardiomyocytes perfused with normal Tyrode's solution which seldom elicited spontaneous AP and did not show after-depolarization and triggered activity.(5)Cardiomyocytes could still generate AP even if the RP was less than-40 mV,this observation is inconsistent with the traditional view.Severe hypokalemia could decrease the RP to less than-40 mV(for example,-34 mV),but cardiomyocytes could still elicit spontaneous APs at the early stage of severe hypokalemia.At the early stage of extream hypokalemia,cardiomyocytes could also elicit spontaneous and smaller APs,but cardiomyocytes finally lose excitability and could not elicit AP at the late stage of extream hypokalemia.Conclusions Hypokalemia has a bidirectional effect on the RP,moderate hypokalemia increased the RP,while severe and extreme hypokalemia increased then decreased the RP.Moderate hypokalemia does not significantly affect the depolarization of AP,but severe and extreme hypokalemia dramatically suppresses the depolarization and even eliminates the excitability.Moderate hypokalemia speeds up the early and middle repolarization,but delays the late-stage repolarization.The onset probabilities of spontaneous excitation,after-depolarization and triggered activity increase athypokalemia.Cardiomyocytes can generate AP at RP of<-40 mV observed at the early stage of severe and extreme hypokalemia,a phenomenon which is inconsistent with the traditional view.These observations are helpful in clarifying the effects and some ambiguous and vague understandings of hypokalemia on myocardial electrophysiology.