Post-transcriptional silencing of SCN1B and SCN2B genes modulates late sodium current in cardiac myocytes from normal dogs and dogs with chronic heart failure

Abstract

Mishra S, Undrovinas NA, Maltsev VA, Reznikov V, Sabbah HN, Undrovinas A. Post-transcriptional silencing of SCN1B and SCN2B genes modulates late sodium current in cardiac myocytes from normal dogs and dogs with chronic heart failure. Am J Physiol Heart Circ Physiol 301: H1596 -H1605, 2011. First published June 24, 2011 doi:10.1152/ajpheart.00948.2009.-The emerging paradigm for Na ϩ current in heart failure (HF) is that its transient component (INaT) responsible for the action potential (AP) upstroke is decreased, whereas the late component (INaL) involved in AP plateau is augmented. Here we tested whether Nav␤1-and Nav␤2-subunits can modulate INaL parameters in normal and failing ventricular cardiomyocytes (VCMs). Chronic HF was produced in nine dogs by multiple sequential coronary artery microembolizations, and six dogs served as a control. INa and APs were measured by the whole cell and perforated patch-clamp in freshly isolated and cultured VCMs, respectively. INaL was augmented with slower decay in HF VCMs compared with normal heart VCMs, and these properties remained unchanged within 5 days of culture. Posttranscriptional silencing SCN1B and SCN2B were achieved by virally delivered short interfering RNA (siRNA) specific to Nav␤1 and Nav␤2. The delivery and efficiency of siRNA were evaluated by green fluorescent protein expression, by the real-time RT-PCR, and Western blots, respectively. Five days after infection, the levels of mRNA and protein for Nav␤1 and Nav␤2 were reduced by Ͼ80%, but mRNA and protein of Nav1.5, as well as INaT, remained unchanged in HF VCMs. Nav␤1-siRNA reduced INaL density and accelerated INaL two-exponential decay, whereas Nav␤2-siRNA produced an opposite effect in VCMs from both normal and failing hearts. Physiological importance of the discovered INaL modulation to affect AP shape and duration was illustrated both experimentally and by numerical simulations of a VCM excitationcontraction coupling model. We conclude that in myocytes of normal and failing dog hearts Nav␤1 and Nav␤2 exhibit oppositely directed modulation of INaL. action potential; in silico simulation THE EMERGING PARADIGM FOR Na ϩ current (I Na ) in chronic heart failure (HF) is that its transient component (I NaT ) responsible for the action potential (AP) upstroke and excitation propagation is decreased, whereas the late component (I NaL ) involved in AP plateau is augmented (21,23,25,42,45,48). Molecular mechanisms of these HF-related I Na alterations are still understudied. Numerous studies indicate a possible role of Na v ␤ auxiliary subunits to modulate Na ϩ channel (NaCh) expression and function (27), but implications of Na v ␤ in I NaL modulation have not been studied in detail, especially in HF. Our previous studies in a canine chronic HF model showed that the protein level of the main NaCh isoform expressed in the heart, Na v 1.5, underlying I NaL (18), is reduced but remains unchanged for Na v ␤ 1 -and Na v ␤ 2 -subunits, making these ␤-subunits relatively upregulated (48). Thus an intriguing possibility...

Redox Control of Cardiac Excitability

“…The effects of ROS on b-subunits have not been studied as far as we know. However, in one study, experimental heart failure in dogs caused increased I NaL due to slower decay, and this effect was concluded to be due to dysfunctioning of the b1-subunits (186). Regarding this study, it is to note that HF causes increased ROS generation in the FIG.…”

Ca2+/Calmodulin-dependent Protein Kinase II (CaMKII) Regulates Cardiac Sodium Channel NaV1.5 Gating by Multiple Phosphorylation Sites

“…We also assayed for CaMKII-induced changes in recovery from inactivation but did not observe a significant difference across tested conditions (data not shown). Again, this may reflect the importance of regulatory ␤-subunits in modulating recovery from inactivation and other gating phenomenon (30,(43)(44)(45)(46). Although the use of the heterologous expression system limits the number of functional effects observed, all of the CaMKII-induced functional changes in I Na seen in HEK293 cells are consistent with those observed in myocytes under similar recording conditions (8,15), indicating that this reduced system can be used to dissect components of CaMKII-dependent functional changes in Na V 1.5, and suffice for the CaMKII-induced shifts in availability and intermediate inactivation.…”

Post-translational modifications of the cardiac Na channel: contribution of CaMKII-dependent phosphorylation to acquired arrhythmias

“…For example, Maltsev et al (66) showed that the ␤ 1 -subunit (but not ␤ 2 ) modulates I Na,L produced by heterologously expressed Na V 1.5 by slowing its decay and increasing its amplitude relative to the peak current. Recently, they showed that reduced expression of either ␤ 1 -or ␤ 2 -subunits caused a significant loss of function or gain of function of I Na,L , respectively, in both normal and failing canine myocytes (78). However, there are contrasting results on the modulation of I Na,L by ␤-subunits in heterologous and native systems and whether they modulate similarly cardiac and noncardiac isoforms.…”