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      Beta-receptor activation increases sodium current in guinea pig heart

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          Abstract

          Aim:

          To study the influence of β-receptor activation on sodium channel current and the physiological significance of increased sodium current with regard to the increased cardiac output caused by sympathetic excitation.

          Methods:

          Multiple experimental approaches, including ECG, action potential recording with conventional microelectrodes, whole-cell current measurements, single-channel recordings, and pumping-force measurements, were applied to guinea pig hearts and isolated ventricular myocytes.

          Results:

          Isoprenaline was found to dose-dependently shorten QRS waves, increase the amplitude and the V max of action potentials, augment the fast sodium current, and increase the occurrence frequencies and open time constants of the long-open and burst modes of the sodium channel. Increased levels of membrane-permeable cAMP have similar effects. In the presence of a calcium channel blocker, TTX reversed the increased pumping force produced by isoprenaline.

          Conclusion:

          Beta-adrenergic modulation increases the inward sodium current and accelerates the conduction velocity within the ventricles by changing the sodium channel modes, which might both be conducive to the synchronous contraction of the heart and enhance its pumping function.

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          Most cited references16

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          Structure and function of voltage-dependent sodium channels: comparison of brain II and cardiac isoforms.

          D Hanck, H Fozzard (1996)
          Cardiac and nerve Na channels have broadly similar functional properties and amino acid sequences, but they demonstrate specific differences in gating, permeation, ionic block, modulation, and pharmacology. Resolution of three-dimensional structures of Na channels is unlikely in the near future, but a number of amino acid sequences from a variety of species and isoforms are known so that channel differences can be exploited to gain insight into the relationship of structure to function. The combination of molecular biology to create chimeras and channels with point mutations and high-resolution electrophysiological techniques to study function encourage the idea that predictions of structure from function are possible. With the goal of understanding the special properties of the cardiac Na channel, this review examines the structural (sequence) similarities between the cardiac and nerve channels and considers what is known about the relationship of structure to function for voltage-dependent Na channels in general and for the cardiac Na channels in particular.
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            Activation of protein kinase A modulates trafficking of the human cardiac sodium channel in Xenopus oocytes.

            Ben A George, Graham K. Murray, Jun Zhou … (2000)
            Voltage-gated Na(+) channels are critical determinants of electrophysiological properties in the heart. Stimulation of beta-adrenergic receptors, which activate cAMP-dependent protein kinase (protein kinase A [PKA]), can alter impulse conduction in normal tissue and promote development of cardiac arrhythmias in pathological states. Recent studies demonstrate that PKA activation increases cardiac Na(+) currents, although the mechanism of this effect is unknown. To explore the molecular basis of Na(+) channel modulation by beta-adrenergic receptors, we have examined the effects of PKA activation on the recombinant human cardiac Na(+) channel, hH1. Both in the absence and the presence of hbeta(1) subunit coexpression, activation of PKA caused a slow increase in Na(+) current that did not saturate despite kinase stimulation for 1 hour. In addition, there was a small shift in the voltage dependence of channel activation and inactivation to more negative voltages. Chloroquine and monensin, compounds that disrupt plasma membrane recycling, reduced hH1 current, suggesting rapid turnover of channels at the cell surface. Preincubation with these agents also prevented the PKA-mediated rise in Na(+) current, indicating that this effect likely resulted from an increased number of Na(+) channels in the plasma membrane. Experiments using chimeric constructs of hH1 and the skeletal muscle Na(+) channel, hSKM1, identified the I-II interdomain loop of hH1 as the region responsible for the PKA effect. These results demonstrate that activation of PKA modulates both trafficking and function of the hH1 channel, with changes in Na(+) current that could either speed or slow conduction, depending on the physiological circumstances.
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              Modulation of rat cardiac sodium channel by the stimulatory G protein alpha subunit.

              William Kabat, Tong Lu, Akihiro Shibata … (1999)
              1. Modulation of cardiac sodium currents (INa) by the G protein stimulatory alpha subunit (Gsalpha) was studied using patch-clamp techniques on freshly dissociated rat ventricular myocytes. 2. Whole-cell recordings showed that stimulation of beta-adrenergic receptors with 10 microM isoprenaline (isoproterenol, ISO) enhanced INa by 68.4 +/- 9.6 % (mean +/- s.e.m.; n = 7, P < 0.05 vs. baseline). With the addition of 22 microgram ml-1 protein kinase A inhibitor (PKI) to the pipette solution, 10 microM ISO enhanced INa by 30.5 +/- 7.0 % (n = 7, P < 0.05 vs. baseline). With the pipette solution containing both PKI and 20 microgram ml-1 anti-Gsalpha IgG or 20 microgram ml-1 anti-Gsalpha IgG alone, 10 microM ISO produced no change in INa. 3. The effect of Gsalpha on INa was not due to changes in the steady-state activation or inactivation curves, the time course of current decay, the development of inactivation, or the recovery from inactivation. 4. Whole-cell INa was increased by 45.2 +/- 5.3% (n = 13, P < 0.05 vs. control) with pipette solution containing 1 microM Gsalpha27-42 peptide (amino acids 27-42 of rat brain Gsalpha) without altering the properties of Na+ channel kinetics. Furthermore, application of 1 nM Gsalpha27-42 to Na+ channels in inside-out macropatches increased the ensemble-averaged INa by 32.5 +/- 6.8 % (n = 8, P < 0.05 vs. baseline). The increase in INa was reversible upon Gsalpha27-42 peptide washout. Single channel experiments showed that the Gsalpha27-42 peptide did not alter the Na+ single channel current amplitude, the mean open time or the mean closed time, but increased the number of functional channels (N) in the patch. 5. Application of selected short amino acid segments (Gsalpha27-36, Gsalpha33-42 and Gsalpha30-39) of the 16 amino acid Gsalpha peptide (Gsalpha27-42 peptide) showed that only the C-terminal segment of this peptide (Gsalpha33-42) significantly increased INa in a dose-dependent fashion. These results show that cardiac INa is regulated by Gsalpha via a mechanism independent of PKA that results in an increase in the number of functional Na+ channels. In addition, a 10 residue domain (amino acids 33-42) near the N-terminus of Gsalpha is important in modulating cardiac Na+ channels.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Acta Pharmacol Sin
                Journal ID (iso-abbrev): Acta Pharmacol. Sin
                Title: Acta Pharmacologica Sinica
                Publisher: Nature Publishing Group
                ISSN (Print): 1671-4083
                ISSN (Electronic): 1745-7254
                Publication date (Print): August 2009
                Publication date (Electronic): 20 July 2009
                Volume: 30
                Issue: 8
                Pages: 1115-1122
                Affiliations
                [1 ]Department of Physiology, Shanghai Jiaotong University School of Medicine , Shanghai 200025, China
                Author notes
                Article
                Publisher Item ID: aps200996
                DOI: 10.1038/aps.2009.96
                PMC ID: 4217312
                PubMed ID: 19617895
                SO-VID: 4c38470b-79b0-463f-bff9-31a291856e0d
                Copyright © Copyright © 2009 CPS and SIMM
                History
                Date received : 22 January 2009
                Date accepted : 05 May 2009
                Categories
                Subject: Original Article

                ScienceOpen disciplines: Pharmacology & Pharmaceutical medicine
                Keywords: sodium-channel current,isoprenaline,camp,single channel recording,action potential,ecg,pumping strength
                Data availability:
                ScienceOpen disciplines: Pharmacology & Pharmaceutical medicine
                Keywords: sodium-channel current, isoprenaline, camp, single channel recording, action potential, ecg, pumping strength

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