Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA056

Poster Communications

Quantitative mass spectrometry-based proteomics determines the uniqueness of the sinus node

M. R. Boyett1, N. Linscheid2, S. Logantha1, P. C. Poulsen2, S. Zhang1, G. Galli1, M. Humphries1, H. Zhang1, J. V. Olsen2, A. Lundby2

1. University of Manchester, Manchester, Lancashire, United Kingdom. 2. University of Copenhagen, Copenhagen, Denmark.

The sinus node is a collection of highly specialised cells that constitute the natural pacemaker of the heart. Although primarily composed of myocytes and fibroblasts like the rest of the heart, the protein expression landscape of the sinus node differs from the surrounding cardiac tissue, endowing it with its unique ability to trigger the heartbeat. Here we performed quantitative proteomics experiments to profile protein expression in the sinus node and compare it to the protein expression in the neighbouring atrial muscle. Sinus node and right atrial biopsies were collected from 30 mice sacrificed in accordance with the Animals (Scientific Procedures) Act, 1986. High-resolution mass spectrometry quantified >7,000 proteins. In the sinus node, the expression of 575 proteins was significantly different from that in the atrial muscle, showing the uniqueness of the tissue. As an example, significant differences were observed in (i) pacemaking ion channels, (ii) contractile proteins linked to sinus node dysfunction, (iii) proteins involved in the storage of lipid (most important source of energy for the heart), (iv) proteins of the important regulatory natriuretic peptide system, (v) transcription factors responsible for the maintenance of the tissue and (vi) the proteins making up an elastic extracellular matrix mechanically supporting and protecting the sinus node. 59 ion channel subunits were detected, including sarcolemmal ion channels, the four major cardiac gap junction channel subunits, and intracellular ion channels (such as the mitochondrial Ca2+ uniporter and the sarcoplasmic reticulum Tric-A/Tmem38a ion channel). The sarcolemmal ion channels include less described channels, such as the store-operated Ca2+ channel (Orai1 and Stim1), Trpm7, purinergic receptor channels (P2rx4 and P2rx7), the two-pore K+ channel, Task-1, and various Cl- channels. Of the sarcolemmal ion channels, the pacemaker channels, HCN4 and HCN1, two important Ca2+ channel accessory subunits (Cavα2δ1 and Cavα2δ2) and the T-type Ca2+ channel, Cav3.2, were significantly more abundant in the sinus node, whereas two K+ channels (Task-1 and Kir3.1) were more highly expressed in the atrial muscle. For the first time, the dataset shows the relative abundance of the ion channels, pumps and exchangers responsible for the pacemaker activity of the sinus node. By computational analysis, we show that the quantified differences in ion channel expression help explain the pacemaker ability of the sinus node. This quantitative proteomics dataset represents the most comprehensive investigation of the sinus node to date and offers a highly detailed insight into the unique composition of the pacemaker of our heart, and is an important resource for understanding sinus node disease.

Where applicable, experiments conform with Society ethical requirements