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In-Depth Study of the Interaction, Sensitivity, and Gating Modulation by PUFAs on K + Channels; Interaction and New Targets

View Article: PubMed Central - PubMed

ABSTRACT

Voltage gated potassium channels (KV) are membrane proteins that allow selective flow of K+ ions in a voltage-dependent manner. These channels play an important role in several excitable cells as neurons, cardiomyocytes, and vascular smooth muscle. Over the last 20 years, it has been shown that omega-3 polyunsaturated fatty acids (PUFAs) enhance or decrease the activity of several cardiac KV channels. PUFAs-dependent modulation of potassium ion channels has been reported to be cardioprotective. However, the precise cellular mechanism underlying the cardiovascular benefits remained unclear in part because new PUFAs targets and signaling pathways continue being discovered. In this review, we will focus on recent data available concerning the following aspects of the KV channel modulation by PUFAs: (i) the exact residues involved in PUFAs-KV channels interaction; (ii) the structural PUFAs determinants important for their effects on KV channels; (iii) the mechanism of the gating modulation of KV channels and, finally, (iv) the PUFAs modulation of a few new targets present in smooth muscle cells (SMC), KCa1.1, K2P, and KATP channels, involved in vascular relaxation.

No MeSH data available.


Related in: MedlinePlus

Topology of a canonical voltage gated ion channel subunit on the lipid bilayer and cartoon representation of the lipoelectric hypothesis mechanism of PUFA-dependent modulation of Shaker-like K+ channels. On the cell membrane four subunits co-assemble to for the ion channel. (A) Each subunit contains six transmembrane segments and N-and C-terminal domains. S1–S4 segments form the voltage sensor and S5–S6 form the ion pore. The S4 segment contains a variable number of positively charged residues known as gating charges that detect small changes on the electric field on the membrane. In response to prolong depolarizations the S4 moves upward perpendicular to the membrane and rotates. (B) This process is called voltage sensor domain activation and it is indicated by the white arrow. Once the four individual S4 are on the upstate the activation gate located at the base intracellular site of the pore domain can open to allow K+ flow (red arrow). A simplified PUFA structure is depicted with the head group located at the extracellular bilayer interface and the bilayer center is depicted in yellow. The PUFA head group interacts electrostatically with the upper gating charges of the S4 promoting mainly channel opening (red arrow). Top and bottom right panels show the front view of the S5 and S6 segments in the closed and open state. Two subunits are depicted for simplicity.
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Figure 2: Topology of a canonical voltage gated ion channel subunit on the lipid bilayer and cartoon representation of the lipoelectric hypothesis mechanism of PUFA-dependent modulation of Shaker-like K+ channels. On the cell membrane four subunits co-assemble to for the ion channel. (A) Each subunit contains six transmembrane segments and N-and C-terminal domains. S1–S4 segments form the voltage sensor and S5–S6 form the ion pore. The S4 segment contains a variable number of positively charged residues known as gating charges that detect small changes on the electric field on the membrane. In response to prolong depolarizations the S4 moves upward perpendicular to the membrane and rotates. (B) This process is called voltage sensor domain activation and it is indicated by the white arrow. Once the four individual S4 are on the upstate the activation gate located at the base intracellular site of the pore domain can open to allow K+ flow (red arrow). A simplified PUFA structure is depicted with the head group located at the extracellular bilayer interface and the bilayer center is depicted in yellow. The PUFA head group interacts electrostatically with the upper gating charges of the S4 promoting mainly channel opening (red arrow). Top and bottom right panels show the front view of the S5 and S6 segments in the closed and open state. Two subunits are depicted for simplicity.

Mentions: The ultimate proof for the specific PUFAs effects on different ion channels came with the identification of the PUFAs binding site on Shaker channels. Because of its lipophilic character and modulatory effects it was proposed that the PUFAs binding site on Shaker K+ channels should be in the vicinity of the gating charges in the voltage sensor (S4 segment) and near residues facing the lipid bilayer (Borjesson et al., 2008). The confirmation for the proposed binding site came quickly. A cysteine scan analysis covering the lipophilic surfaces of the extracellular halves of S3–S6 segment showed that residues I325C and T329C located in the carboxyl end of helix S3, and I360C at S4 were insensitive to DHA. On the contrary, the L366C mutation increased DHA sensitivity of Shaker K+ channels (Borjesson and Elinder, 2011). To further define the PUFAs binding site, positives charges were introduced to each of the above-mentioned residues in the S3–S4 regions by using MTSEA+ reagent. Consistently with the cysteine scan data, a positive charge at residues I325; T329 and A359; I360 of the S3 and S4 respectively resulted in an increased sensitivity to DHA effects (Borjesson and Elinder, 2011). In addition to the experimental data, a structural model built to predict 3D interactions suggested that a negative charge at R1 (R362) would reduce the PUFA effect. Consistently with the model, when the charge of R362C mutant was modified negatively with MTES− reagent the G(V) shift induced by DHA was smaller than that induced in WT Shaker K+ channels. In contrast, R362C+ (exposed to MTSET+) restored PUFA sensitivity. Some KV channels such as KV1.2 have an additional gating charge R0 at the top of the S4 segment. An homology model of the Shaker K+ channel based on the KV1.2/2.1 chimera predicts that a positive residue at that position (A359) could strengthen the interaction between the PUFA head group and the ion channel (Borjesson and Elinder, 2011). When attaching MTSET+ to A359C, the DHA-induced G(V) shift was greater. Experiments in which the charge of R0 and R1 was changed support the proposed localization of the PUFA binding site and suggested that different PUFAs should have very different effects in modulating different ion channels depending on the presence of a charge at positions R0 and/or R1 (Borjesson and Elinder, 2011). Together, the data showed that high impact residues for DHA on Shaker K+ channels are clustered in a small region of the lipid facing S3–S4 corner of the voltage sensor domain but distant from the pore region (Figure 2). Positive charges located close to the PUFAs binding site increase PUFA potency.


In-Depth Study of the Interaction, Sensitivity, and Gating Modulation by PUFAs on K + Channels; Interaction and New Targets
Topology of a canonical voltage gated ion channel subunit on the lipid bilayer and cartoon representation of the lipoelectric hypothesis mechanism of PUFA-dependent modulation of Shaker-like K+ channels. On the cell membrane four subunits co-assemble to for the ion channel. (A) Each subunit contains six transmembrane segments and N-and C-terminal domains. S1–S4 segments form the voltage sensor and S5–S6 form the ion pore. The S4 segment contains a variable number of positively charged residues known as gating charges that detect small changes on the electric field on the membrane. In response to prolong depolarizations the S4 moves upward perpendicular to the membrane and rotates. (B) This process is called voltage sensor domain activation and it is indicated by the white arrow. Once the four individual S4 are on the upstate the activation gate located at the base intracellular site of the pore domain can open to allow K+ flow (red arrow). A simplified PUFA structure is depicted with the head group located at the extracellular bilayer interface and the bilayer center is depicted in yellow. The PUFA head group interacts electrostatically with the upper gating charges of the S4 promoting mainly channel opening (red arrow). Top and bottom right panels show the front view of the S5 and S6 segments in the closed and open state. Two subunits are depicted for simplicity.
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Related In: Results  -  Collection

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Figure 2: Topology of a canonical voltage gated ion channel subunit on the lipid bilayer and cartoon representation of the lipoelectric hypothesis mechanism of PUFA-dependent modulation of Shaker-like K+ channels. On the cell membrane four subunits co-assemble to for the ion channel. (A) Each subunit contains six transmembrane segments and N-and C-terminal domains. S1–S4 segments form the voltage sensor and S5–S6 form the ion pore. The S4 segment contains a variable number of positively charged residues known as gating charges that detect small changes on the electric field on the membrane. In response to prolong depolarizations the S4 moves upward perpendicular to the membrane and rotates. (B) This process is called voltage sensor domain activation and it is indicated by the white arrow. Once the four individual S4 are on the upstate the activation gate located at the base intracellular site of the pore domain can open to allow K+ flow (red arrow). A simplified PUFA structure is depicted with the head group located at the extracellular bilayer interface and the bilayer center is depicted in yellow. The PUFA head group interacts electrostatically with the upper gating charges of the S4 promoting mainly channel opening (red arrow). Top and bottom right panels show the front view of the S5 and S6 segments in the closed and open state. Two subunits are depicted for simplicity.
Mentions: The ultimate proof for the specific PUFAs effects on different ion channels came with the identification of the PUFAs binding site on Shaker channels. Because of its lipophilic character and modulatory effects it was proposed that the PUFAs binding site on Shaker K+ channels should be in the vicinity of the gating charges in the voltage sensor (S4 segment) and near residues facing the lipid bilayer (Borjesson et al., 2008). The confirmation for the proposed binding site came quickly. A cysteine scan analysis covering the lipophilic surfaces of the extracellular halves of S3–S6 segment showed that residues I325C and T329C located in the carboxyl end of helix S3, and I360C at S4 were insensitive to DHA. On the contrary, the L366C mutation increased DHA sensitivity of Shaker K+ channels (Borjesson and Elinder, 2011). To further define the PUFAs binding site, positives charges were introduced to each of the above-mentioned residues in the S3–S4 regions by using MTSEA+ reagent. Consistently with the cysteine scan data, a positive charge at residues I325; T329 and A359; I360 of the S3 and S4 respectively resulted in an increased sensitivity to DHA effects (Borjesson and Elinder, 2011). In addition to the experimental data, a structural model built to predict 3D interactions suggested that a negative charge at R1 (R362) would reduce the PUFA effect. Consistently with the model, when the charge of R362C mutant was modified negatively with MTES− reagent the G(V) shift induced by DHA was smaller than that induced in WT Shaker K+ channels. In contrast, R362C+ (exposed to MTSET+) restored PUFA sensitivity. Some KV channels such as KV1.2 have an additional gating charge R0 at the top of the S4 segment. An homology model of the Shaker K+ channel based on the KV1.2/2.1 chimera predicts that a positive residue at that position (A359) could strengthen the interaction between the PUFA head group and the ion channel (Borjesson and Elinder, 2011). When attaching MTSET+ to A359C, the DHA-induced G(V) shift was greater. Experiments in which the charge of R0 and R1 was changed support the proposed localization of the PUFA binding site and suggested that different PUFAs should have very different effects in modulating different ion channels depending on the presence of a charge at positions R0 and/or R1 (Borjesson and Elinder, 2011). Together, the data showed that high impact residues for DHA on Shaker K+ channels are clustered in a small region of the lipid facing S3–S4 corner of the voltage sensor domain but distant from the pore region (Figure 2). Positive charges located close to the PUFAs binding site increase PUFA potency.

View Article: PubMed Central - PubMed

ABSTRACT

Voltage gated potassium channels (KV) are membrane proteins that allow selective flow of K+ ions in a voltage-dependent manner. These channels play an important role in several excitable cells as neurons, cardiomyocytes, and vascular smooth muscle. Over the last 20 years, it has been shown that omega-3 polyunsaturated fatty acids (PUFAs) enhance or decrease the activity of several cardiac KV channels. PUFAs-dependent modulation of potassium ion channels has been reported to be cardioprotective. However, the precise cellular mechanism underlying the cardiovascular benefits remained unclear in part because new PUFAs targets and signaling pathways continue being discovered. In this review, we will focus on recent data available concerning the following aspects of the KV channel modulation by PUFAs: (i) the exact residues involved in PUFAs-KV channels interaction; (ii) the structural PUFAs determinants important for their effects on KV channels; (iii) the mechanism of the gating modulation of KV channels and, finally, (iv) the PUFAs modulation of a few new targets present in smooth muscle cells (SMC), KCa1.1, K2P, and KATP channels, involved in vascular relaxation.

No MeSH data available.


Related in: MedlinePlus