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The involvement of TRPC3 channels in sinoatrial arrhythmias.

Ju YK, Lee BH, Trajanovska S, Hao G, Allen DG, Lei M, Cannell MB - Front Physiol (2015)

Bottom Line: We will then present some of our recent research progress in this field.Our experiments results suggest that pacing-induced AF in angiotensin II (Ang II) treated mice are significantly reduced in mice lacking the TRPC3 gene (TRPC3(-/-) mice) compared to wild type controls.We also show that pacemaker cells express TRPC3 and several other molecular components related to SOCE/ROCE signaling, including STIM1 and IP3R.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia.

ABSTRACT
Atrial fibrillation (AF) is a significant contributor to cardiovascular morbidity and mortality. The currently available treatments are limited and AF continues to be a major clinical challenge. Clinical studies have shown that AF is frequently associated with dysfunction in the sino-atrial node (SAN). The association between AF and SAN dysfunction is probably related to the communication between the SAN and the surrounding atrial cells that form the SAN-atrial pacemaker complex and/or pathological processes that affect both the SAN and atrial simultaneously. Recent evidence suggests that Ca(2+) entry through TRPC3 (Transient Receptor Potential Canonical-3) channels may underlie several pathophysiological conditions -including cardiac arrhythmias. However, it is still not known if atrial and sinoatrial node cells are also involved. In this article we will first briefly review TRPC3 and IP3R signaling that relate to store/receptor-operated Ca(2+) entry (SOCE/ROCE) mechanisms and cardiac arrhythmias. We will then present some of our recent research progress in this field. Our experiments results suggest that pacing-induced AF in angiotensin II (Ang II) treated mice are significantly reduced in mice lacking the TRPC3 gene (TRPC3(-/-) mice) compared to wild type controls. We also show that pacemaker cells express TRPC3 and several other molecular components related to SOCE/ROCE signaling, including STIM1 and IP3R. Activation of G-protein coupled receptors (GPCRs) signaling that is able to modulate SOCE/ROCE and Ang II induced Ca(2+) homeostasis changes in sinoatrial complex being linked to TRPC3. The results provide new evidence that TRPC3 may play a role in sinoatrial and atrial arrhythmias that are caused by GPCRs activation.

No MeSH data available.


Related in: MedlinePlus

The effect of Pyr10 on intracellular Ca2+ after application of 1-oleoy1-2-acyl-sn-glycerol (OAG) 100 μM. The intact SANs were loaded with Ca2+ indicator indo-1. (A,B) show intracellular Ca2+ recordings from a WT mouse. (B,C) The statistics pool data shows percentage changes in resting Ca2+, Ca2+ transient and firing rate in WT and TRPC3 KO mice respectively. (B) OAG treatment against control. (C) 2 μM Pyr10 treatment against OAG treatment. *P < 0.05.
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Figure 6: The effect of Pyr10 on intracellular Ca2+ after application of 1-oleoy1-2-acyl-sn-glycerol (OAG) 100 μM. The intact SANs were loaded with Ca2+ indicator indo-1. (A,B) show intracellular Ca2+ recordings from a WT mouse. (B,C) The statistics pool data shows percentage changes in resting Ca2+, Ca2+ transient and firing rate in WT and TRPC3 KO mice respectively. (B) OAG treatment against control. (C) 2 μM Pyr10 treatment against OAG treatment. *P < 0.05.

Mentions: Figure 5 shows action potentials recorded from an intact sinoatrial node preparation using conventional intracellular recording techniques. After application of 1 μM Ang II for 30 min, there was an increase in pacemaker firing rate associated with a depolarised membrane potential (Figure 5B). Application of 2 μM Pyr10 for 20 min, slowed pacemaker firing rate with maximum diastolic potential returning to the control level (Figure 5C). Application of 20 μM Pyr10 further reduced firing rate within 7 min (Figure 5D). These results suggest that the membrane depolarization caused by Ang II could be reversed by the TRPC3 channel blocker. The results also support the idea that TRPC3 could be a channel that produces an inward current after GPCR activation by Ang II (Onohara et al., 2006). Importantly, and in contrast to WT mice, the pacemaker firing rate and action potential depolarization were not affected by Ang II and this response not significantly altered by application of Pyr10 to SAN from TRPC3 KO mice (Figures 5E–H). This is consistent with pacing induced AF in mice treated with Ang II being reduced in TRPC3−/− mice. (Figure 2) Therefore, these results strongly suggest that Pyr10 not only specifically blocked TRPC3 channels but that TRPC3 also contributes to pacemaker activity. To further investigate if the changes in pacemaker activity were related to Ca2+ entry through ROCE we examined intracellular Ca2+ changes caused by OAG and the effect of Pyr10. Figure 6Aa shows a representative intracellular Ca2+ signal recorded from a WT intact sinoatrial preparation loaded with the Ca2+ indicator indo-1. Both resting Ca2+ and Ca2+ transients were increased after 20 min application of 100 μM OAG (Figure 6Ab). Resting Ca2+ returned to the control level associated with a slowed firing rate after application of 2 μM Pyr10 for 15 min (Figure 6Ac). Further slowing and irregular pacemaker activity was apparent when the concentration of Pyr10 was increased to 20 μM for 15 min as shown in Figure 6Ad. On average, resting Ca2+ increased by 20.2 ± 6.9% (P = 0.023, n = 5); the Ca2+ transient also increased by 26.1 ± 5.6% (p = 0.003, n = 5) and was associated with a 13.9% increase in pacemaker firing rate (p = 0.005, n = 5,) in response to OAG treatment. There no significant changes by OAG in TRPC3 KO groups (n = 4) as shown in Figure 6B. The results further confirmed that TRPC3 was involved in OAG produced Ca2+ entry through ROCE upon GPCR activation. 2 μM Pyr10 significantly reduced the resting Ca2+ elevation produced by OAG treatment in WT but not in TRPC3 KO mice (Figure 6C). Unexpectedly, PyR10 produced no significant changes in Ca2+ transient amplitude and firing rate in both groups after exposure to OAG. The results indicated that Ca2+ entry through ROCE appeared to mainly influence resting Ca2+ in pacemaker cells and the lack of effect of PYR10 after OAG stimulation on the Ca2+ transient and pacemaker firing rate may reflect additional effect(s) of PyR10 beyond TRPC3. In support of the latter idea, 20 μM Pyr10 reduced the amplitude of the Ca2+ transient in TRPC3 KO mice without significantly changing pacemaker firing rate or resting Ca2+ level (data not show).


The involvement of TRPC3 channels in sinoatrial arrhythmias.

Ju YK, Lee BH, Trajanovska S, Hao G, Allen DG, Lei M, Cannell MB - Front Physiol (2015)

The effect of Pyr10 on intracellular Ca2+ after application of 1-oleoy1-2-acyl-sn-glycerol (OAG) 100 μM. The intact SANs were loaded with Ca2+ indicator indo-1. (A,B) show intracellular Ca2+ recordings from a WT mouse. (B,C) The statistics pool data shows percentage changes in resting Ca2+, Ca2+ transient and firing rate in WT and TRPC3 KO mice respectively. (B) OAG treatment against control. (C) 2 μM Pyr10 treatment against OAG treatment. *P < 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4373262&req=5

Figure 6: The effect of Pyr10 on intracellular Ca2+ after application of 1-oleoy1-2-acyl-sn-glycerol (OAG) 100 μM. The intact SANs were loaded with Ca2+ indicator indo-1. (A,B) show intracellular Ca2+ recordings from a WT mouse. (B,C) The statistics pool data shows percentage changes in resting Ca2+, Ca2+ transient and firing rate in WT and TRPC3 KO mice respectively. (B) OAG treatment against control. (C) 2 μM Pyr10 treatment against OAG treatment. *P < 0.05.
Mentions: Figure 5 shows action potentials recorded from an intact sinoatrial node preparation using conventional intracellular recording techniques. After application of 1 μM Ang II for 30 min, there was an increase in pacemaker firing rate associated with a depolarised membrane potential (Figure 5B). Application of 2 μM Pyr10 for 20 min, slowed pacemaker firing rate with maximum diastolic potential returning to the control level (Figure 5C). Application of 20 μM Pyr10 further reduced firing rate within 7 min (Figure 5D). These results suggest that the membrane depolarization caused by Ang II could be reversed by the TRPC3 channel blocker. The results also support the idea that TRPC3 could be a channel that produces an inward current after GPCR activation by Ang II (Onohara et al., 2006). Importantly, and in contrast to WT mice, the pacemaker firing rate and action potential depolarization were not affected by Ang II and this response not significantly altered by application of Pyr10 to SAN from TRPC3 KO mice (Figures 5E–H). This is consistent with pacing induced AF in mice treated with Ang II being reduced in TRPC3−/− mice. (Figure 2) Therefore, these results strongly suggest that Pyr10 not only specifically blocked TRPC3 channels but that TRPC3 also contributes to pacemaker activity. To further investigate if the changes in pacemaker activity were related to Ca2+ entry through ROCE we examined intracellular Ca2+ changes caused by OAG and the effect of Pyr10. Figure 6Aa shows a representative intracellular Ca2+ signal recorded from a WT intact sinoatrial preparation loaded with the Ca2+ indicator indo-1. Both resting Ca2+ and Ca2+ transients were increased after 20 min application of 100 μM OAG (Figure 6Ab). Resting Ca2+ returned to the control level associated with a slowed firing rate after application of 2 μM Pyr10 for 15 min (Figure 6Ac). Further slowing and irregular pacemaker activity was apparent when the concentration of Pyr10 was increased to 20 μM for 15 min as shown in Figure 6Ad. On average, resting Ca2+ increased by 20.2 ± 6.9% (P = 0.023, n = 5); the Ca2+ transient also increased by 26.1 ± 5.6% (p = 0.003, n = 5) and was associated with a 13.9% increase in pacemaker firing rate (p = 0.005, n = 5,) in response to OAG treatment. There no significant changes by OAG in TRPC3 KO groups (n = 4) as shown in Figure 6B. The results further confirmed that TRPC3 was involved in OAG produced Ca2+ entry through ROCE upon GPCR activation. 2 μM Pyr10 significantly reduced the resting Ca2+ elevation produced by OAG treatment in WT but not in TRPC3 KO mice (Figure 6C). Unexpectedly, PyR10 produced no significant changes in Ca2+ transient amplitude and firing rate in both groups after exposure to OAG. The results indicated that Ca2+ entry through ROCE appeared to mainly influence resting Ca2+ in pacemaker cells and the lack of effect of PYR10 after OAG stimulation on the Ca2+ transient and pacemaker firing rate may reflect additional effect(s) of PyR10 beyond TRPC3. In support of the latter idea, 20 μM Pyr10 reduced the amplitude of the Ca2+ transient in TRPC3 KO mice without significantly changing pacemaker firing rate or resting Ca2+ level (data not show).

Bottom Line: We will then present some of our recent research progress in this field.Our experiments results suggest that pacing-induced AF in angiotensin II (Ang II) treated mice are significantly reduced in mice lacking the TRPC3 gene (TRPC3(-/-) mice) compared to wild type controls.We also show that pacemaker cells express TRPC3 and several other molecular components related to SOCE/ROCE signaling, including STIM1 and IP3R.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia.

ABSTRACT
Atrial fibrillation (AF) is a significant contributor to cardiovascular morbidity and mortality. The currently available treatments are limited and AF continues to be a major clinical challenge. Clinical studies have shown that AF is frequently associated with dysfunction in the sino-atrial node (SAN). The association between AF and SAN dysfunction is probably related to the communication between the SAN and the surrounding atrial cells that form the SAN-atrial pacemaker complex and/or pathological processes that affect both the SAN and atrial simultaneously. Recent evidence suggests that Ca(2+) entry through TRPC3 (Transient Receptor Potential Canonical-3) channels may underlie several pathophysiological conditions -including cardiac arrhythmias. However, it is still not known if atrial and sinoatrial node cells are also involved. In this article we will first briefly review TRPC3 and IP3R signaling that relate to store/receptor-operated Ca(2+) entry (SOCE/ROCE) mechanisms and cardiac arrhythmias. We will then present some of our recent research progress in this field. Our experiments results suggest that pacing-induced AF in angiotensin II (Ang II) treated mice are significantly reduced in mice lacking the TRPC3 gene (TRPC3(-/-) mice) compared to wild type controls. We also show that pacemaker cells express TRPC3 and several other molecular components related to SOCE/ROCE signaling, including STIM1 and IP3R. Activation of G-protein coupled receptors (GPCRs) signaling that is able to modulate SOCE/ROCE and Ang II induced Ca(2+) homeostasis changes in sinoatrial complex being linked to TRPC3. The results provide new evidence that TRPC3 may play a role in sinoatrial and atrial arrhythmias that are caused by GPCRs activation.

No MeSH data available.


Related in: MedlinePlus