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Differential regulation of proton-sensitive ion channels by phospholipids: a comparative study between ASICs and TRPV1.

Kweon HJ, Yu SY, Kim DI, Suh BC - PLoS ONE (2015)

Bottom Line: We observed that ASICs do not require membrane phosphatidylinositol 4-phosphate (PI(4)P) or phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) for their function.Finally, we compared the effects of arachidonic acid (AA) on two proton-sensitive ion channels.In conclusion, ASICs and TRPV1 have different sensitivities toward membrane phospholipids, such as PI(4)P, PI(4,5)P2, and AA, although they have common roles as proton sensors.

View Article: PubMed Central - PubMed

Affiliation: Department of Brain Science, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Republic of Korea.

ABSTRACT
Protons are released in pain-generating pathological conditions such as inflammation, ischemic stroke, infection, and cancer. During normal synaptic activities, protons are thought to play a role in neurotransmission processes. Acid-sensing ion channels (ASICs) are typical proton sensors in the central nervous system (CNS) and the peripheral nervous system (PNS). In addition to ASICs, capsaicin- and heat-activated transient receptor potential vanilloid 1 (TRPV1) channels can also mediate proton-mediated pain signaling. In spite of their importance in perception of pH fluctuations, the regulatory mechanisms of these proton-sensitive ion channels still need to be further investigated. Here, we compared regulation of ASICs and TRPV1 by membrane phosphoinositides, which are general cofactors of many receptors and ion channels. We observed that ASICs do not require membrane phosphatidylinositol 4-phosphate (PI(4)P) or phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) for their function. However, TRPV1 currents were inhibited by simultaneous breakdown of PI(4)P and PI(4,5)P2. By using a novel chimeric protein, CF-PTEN, that can specifically dephosphorylate at the D3 position of phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3), we also observed that neither ASICs nor TRPV1 activities were altered by depletion of PI(3,4,5)P3 in intact cells. Finally, we compared the effects of arachidonic acid (AA) on two proton-sensitive ion channels. We observed that AA potentiates the currents of both ASICs and TRPV1, but that they have different recovery aspects. In conclusion, ASICs and TRPV1 have different sensitivities toward membrane phospholipids, such as PI(4)P, PI(4,5)P2, and AA, although they have common roles as proton sensors. Further investigation about the complementary roles and respective contributions of ASICs and TRPV1 in proton-mediated signaling is necessary.

No MeSH data available.


Related in: MedlinePlus

Heteromeric ASIC currents are insensitive to PI(4)P and PI(4,5)P2.(A) Current traces from ASIC1a/2a, ASIC1a/3, and ASIC2a/3 heteromeric channels evoked by extracellular acidification in cells expressing LDR and PJ. Rapamycin (1 μM) was bath-applied for 60 s, and then normal extracellular solution was perfused for 10 s right before the second pulse to minimize possible side effects of rapamycin. Dashed line indicates the zero current level. (B) Relative current density measured for the currents of ASIC1a/2a and ASIC1a/3 in (A) (n = 3, respectively). Current density of each pulse was divided by that of the first pulse. There is no statistical significance with two-way ANOVA followed by Bonferroni post-hoc test. (C) Relative current density measured for the transient and sustained currents of ASIC2a/3 in (A) (n = 3 for PJ-Dead; n = 5 for PJ). There is no statistical significance with two-way ANOVA followed by Bonferroni post-hoc test. Data are mean ± SEM.
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pone.0122014.g003: Heteromeric ASIC currents are insensitive to PI(4)P and PI(4,5)P2.(A) Current traces from ASIC1a/2a, ASIC1a/3, and ASIC2a/3 heteromeric channels evoked by extracellular acidification in cells expressing LDR and PJ. Rapamycin (1 μM) was bath-applied for 60 s, and then normal extracellular solution was perfused for 10 s right before the second pulse to minimize possible side effects of rapamycin. Dashed line indicates the zero current level. (B) Relative current density measured for the currents of ASIC1a/2a and ASIC1a/3 in (A) (n = 3, respectively). Current density of each pulse was divided by that of the first pulse. There is no statistical significance with two-way ANOVA followed by Bonferroni post-hoc test. (C) Relative current density measured for the transient and sustained currents of ASIC2a/3 in (A) (n = 3 for PJ-Dead; n = 5 for PJ). There is no statistical significance with two-way ANOVA followed by Bonferroni post-hoc test. Data are mean ± SEM.

Mentions: We also tested whether heteromeric ASICs have dependence on phosphoinositides for their function, since most ASICs exist as heteromeric channels in physiological conditions [42–44]. The current traces from heteromeric channels of ASIC1a/2a, ASIC1a/3, and ASIC2a/3 were similar to those of a previous study [45]. Recruitment of PJ to the PM had no significant effects on either ASIC1a/2a or ASIC1a/3 heteromeric channels (Fig. 3A-B), and transient and sustained currents of ASIC2a/3 heteromeric channels were not significantly affected by the application of rapamycin (Fig. 3A and C). In conclusion, neither homomeric ASICs nor heteromeric ASICs require phosphoinositides for their activities.


Differential regulation of proton-sensitive ion channels by phospholipids: a comparative study between ASICs and TRPV1.

Kweon HJ, Yu SY, Kim DI, Suh BC - PLoS ONE (2015)

Heteromeric ASIC currents are insensitive to PI(4)P and PI(4,5)P2.(A) Current traces from ASIC1a/2a, ASIC1a/3, and ASIC2a/3 heteromeric channels evoked by extracellular acidification in cells expressing LDR and PJ. Rapamycin (1 μM) was bath-applied for 60 s, and then normal extracellular solution was perfused for 10 s right before the second pulse to minimize possible side effects of rapamycin. Dashed line indicates the zero current level. (B) Relative current density measured for the currents of ASIC1a/2a and ASIC1a/3 in (A) (n = 3, respectively). Current density of each pulse was divided by that of the first pulse. There is no statistical significance with two-way ANOVA followed by Bonferroni post-hoc test. (C) Relative current density measured for the transient and sustained currents of ASIC2a/3 in (A) (n = 3 for PJ-Dead; n = 5 for PJ). There is no statistical significance with two-way ANOVA followed by Bonferroni post-hoc test. Data are mean ± SEM.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4362947&req=5

pone.0122014.g003: Heteromeric ASIC currents are insensitive to PI(4)P and PI(4,5)P2.(A) Current traces from ASIC1a/2a, ASIC1a/3, and ASIC2a/3 heteromeric channels evoked by extracellular acidification in cells expressing LDR and PJ. Rapamycin (1 μM) was bath-applied for 60 s, and then normal extracellular solution was perfused for 10 s right before the second pulse to minimize possible side effects of rapamycin. Dashed line indicates the zero current level. (B) Relative current density measured for the currents of ASIC1a/2a and ASIC1a/3 in (A) (n = 3, respectively). Current density of each pulse was divided by that of the first pulse. There is no statistical significance with two-way ANOVA followed by Bonferroni post-hoc test. (C) Relative current density measured for the transient and sustained currents of ASIC2a/3 in (A) (n = 3 for PJ-Dead; n = 5 for PJ). There is no statistical significance with two-way ANOVA followed by Bonferroni post-hoc test. Data are mean ± SEM.
Mentions: We also tested whether heteromeric ASICs have dependence on phosphoinositides for their function, since most ASICs exist as heteromeric channels in physiological conditions [42–44]. The current traces from heteromeric channels of ASIC1a/2a, ASIC1a/3, and ASIC2a/3 were similar to those of a previous study [45]. Recruitment of PJ to the PM had no significant effects on either ASIC1a/2a or ASIC1a/3 heteromeric channels (Fig. 3A-B), and transient and sustained currents of ASIC2a/3 heteromeric channels were not significantly affected by the application of rapamycin (Fig. 3A and C). In conclusion, neither homomeric ASICs nor heteromeric ASICs require phosphoinositides for their activities.

Bottom Line: We observed that ASICs do not require membrane phosphatidylinositol 4-phosphate (PI(4)P) or phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) for their function.Finally, we compared the effects of arachidonic acid (AA) on two proton-sensitive ion channels.In conclusion, ASICs and TRPV1 have different sensitivities toward membrane phospholipids, such as PI(4)P, PI(4,5)P2, and AA, although they have common roles as proton sensors.

View Article: PubMed Central - PubMed

Affiliation: Department of Brain Science, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Republic of Korea.

ABSTRACT
Protons are released in pain-generating pathological conditions such as inflammation, ischemic stroke, infection, and cancer. During normal synaptic activities, protons are thought to play a role in neurotransmission processes. Acid-sensing ion channels (ASICs) are typical proton sensors in the central nervous system (CNS) and the peripheral nervous system (PNS). In addition to ASICs, capsaicin- and heat-activated transient receptor potential vanilloid 1 (TRPV1) channels can also mediate proton-mediated pain signaling. In spite of their importance in perception of pH fluctuations, the regulatory mechanisms of these proton-sensitive ion channels still need to be further investigated. Here, we compared regulation of ASICs and TRPV1 by membrane phosphoinositides, which are general cofactors of many receptors and ion channels. We observed that ASICs do not require membrane phosphatidylinositol 4-phosphate (PI(4)P) or phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) for their function. However, TRPV1 currents were inhibited by simultaneous breakdown of PI(4)P and PI(4,5)P2. By using a novel chimeric protein, CF-PTEN, that can specifically dephosphorylate at the D3 position of phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3), we also observed that neither ASICs nor TRPV1 activities were altered by depletion of PI(3,4,5)P3 in intact cells. Finally, we compared the effects of arachidonic acid (AA) on two proton-sensitive ion channels. We observed that AA potentiates the currents of both ASICs and TRPV1, but that they have different recovery aspects. In conclusion, ASICs and TRPV1 have different sensitivities toward membrane phospholipids, such as PI(4)P, PI(4,5)P2, and AA, although they have common roles as proton sensors. Further investigation about the complementary roles and respective contributions of ASICs and TRPV1 in proton-mediated signaling is necessary.

No MeSH data available.


Related in: MedlinePlus