Inhibition of the Magnesium-Sensitive TRPM7-like Channel in Cardiac Myocytes by Nonhydrolysable GTP Analogs: Involvement of Phosphoinositide Metabolism

Mačianskienė, Regina; Gwanyanya, Asfree; Vereecke, Johan; Mubagwa, Kanigula

doi:10.1159/000149788

Cited by 18 publications

(22 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Similar to potassium channels (8), TRPM7 channel activity is diminished during prolonged patch-clamp recording and can be recovered when PI(4,5)P 2 is applied to the inner side of the membrane in cell-free patches (22,47). In cardiac myocytes, rundown of whole cell TRPM7-like current is reduced when internal solutions contain micromolar PI(4,5)P 2 (31). Whether both Mg 2ϩ inhibitor sites that we report here involve screening of phosphoinositides or other anionic lipids remains to be discovered.…”

Section: Resultsmentioning

confidence: 99%

Detailed examination of Mg²⁺ and pH sensitivity of human TRPM7 channels

Chokshi

Matsushita

Kozak

2012

American Journal of Physiology-Cell Physiology

116

View full text Add to dashboard Cite

TRPM7 channel kinase is a protein highly expressed in cells of hematopoietic lineage, such as lymphocytes. Studies performed in native and heterologous expression systems have shown that TRPM7 forms nonselective cation channels functional in the plasma membrane and activated on depletion of cellular Mg(2+). In addition to internal Mg(2+), cytosolic pH and the phospholipid phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P(2)] are potent physiological regulators of this channel: protons inhibit, while PI(4,5)P(2) is required for TRPM7 channel activity. These channels are also inhibited from inside by other metal cations and polyamines. While the regulation of TRPM7 channels by internal metal ions, acidic pH, and PI(4,5)P(2) is voltage independent, extracellular metal cations and polyamines block voltage dependently at micromolar concentrations and appear to occupy a distinct blocking site. In the present study we investigated intracellular Mg(2+) and pH dependence of native TRPM7 currents using whole cell patch-clamp electrophysiology in human Jurkat T lymphocytes and HEK293 cells. Our main findings are 1) Mg(2+) inhibition involves not one but two separate sites of high (∼10 μM) and low (∼165 μM) affinity; and 2) while sharing certain characteristics with Mg(2+) inhibition, protons most likely inhibit through one inhibitory site, corresponding to the low-affinity Mg(2+) site, with an estimated IC(50) of pH 6.3. Additionally, we present data on amplitude distribution of preactivated TRPM7 currents in Jurkat T lymphocytes in the absence of prior Mg(2+) or proton depletion.

show abstract

Section: Resultsmentioning

confidence: 99%

Detailed examination of Mg²⁺ and pH sensitivity of human TRPM7 channels

Chokshi

Matsushita

Kozak

2012

American Journal of Physiology-Cell Physiology

116

View full text Add to dashboard Cite

show abstract

“…It is well known from studies on potassium channels of Kir and K v 7 family that channel activity runs down in minutes in inside-out patches (e.g., Refs. 14, 15, 32), but this process is much slower in whole cell recording (21,33). This has been attributed to loss of PI(4,5)P 2 phospholipid in the membrane patches without ATP or other regenerating molecules being present (15).…”

Section: Discussionmentioning

confidence: 99%

Sensitivity of TRPM7 channels to Mg²⁺ characterized in cell-free patches of Jurkat T lymphocytes

Chokshi

Matsushita

Kozak

2012

American Journal of Physiology-Cell Physiology

View full text Add to dashboard Cite

Transient receptor potential melastatin 7 (TRPM7) channels were originally identified electrophysiologically when depletion of cytosolic Mg(2+) resulted in the gradual development of an outwardly rectifying cation current. Conversely, inclusion of millimolar Mg(2+) in internal solutions prevented activation of these channels in whole cell patch clamp. We recently demonstrated that the Jurkat T-cell whole cell TRPM7 channels are inhibited by internal Mg(2+) in a biphasic manner, displaying high [IC(50(1)) ≈ 10 μM] and low [IC(50(2)) ≈ 165 μM] affinity inhibitor sites. In that study, we had characterized the dependence of the maximum cell current density on intracellular Mg(2+) concentration. To characterize Mg(2+) inhibition in Jurkat T cells in more detail and compare it to whole cell results, we recorded single TRPM7 channels in cell-free membrane patches and investigated the dependence of their activity on Mg(2+) added on the cytoplasmic side. We systematically varied free Mg(2+) from 265 nM to 407 μM and evaluated the extent of channel inhibition in inside-out patch for 58 patches. We found that the TRPM7 channel shows two conductance levels of 39.0 pS (γ(1)) and 18.6 pS (γ(2)) and that both are reversibly inhibited by internal Mg(2+). The 39.0-pS conductance is the dominant state of the channel, observed most frequently in this recording configuration. The dose-response relation in inside-out patches shows a steeper Mg(2+) dependence than in whole cell, yielding IC(50(1)) of 25.1 μM and IC(50(2)) of 91.2 μM.. Single-channel analysis shows that the primary effect of Mg(2+) in multichannel patches is a reversible reduction of the number of conducting channels (N(o)). Additionally, at high Mg(2+) concentrations, we observed a saturating 20% reduction in unitary conductance (γ(1)). Thus Mg(2+) inhibition in whole cell can be explained by a drop in individual participating channels and a modest reduction in conductance. We also found that TRPM7 channels in some patches were not sensitive to this ion at submaximal Mg(2+) concentrations. Interestingly, Mg(2+) inhibition showed the property of use dependence: with repeated applications, Mg(2+) effect became gradually more potent, which suggests that Mg(2+) sensitivity of the channel is a dynamic characteristic that depends on other membrane factors.

show abstract

“…Co-overexpression of muscarinic receptor 1 and TRPM7 in HEK293 cells followed by charbacol stimulation leads to TRPM7 inactivation due to depletion of PIP 2 in the plasma membrane (Runnels et al 2002). Endogenous TRPM7 in CA1 hippocampal neurons is sensitive to nerve growth factor via a PLC-dependent pathway (Tian et al 2007), and in cardiac myocytes GTP analogues lead to TRPM7 inhibition through G-protein activity and PIP 2 metabolism (Macianskiene et al 2008). In contrast, moderate overexpression of TRPM7 in neuroblastoma N1E-115 cells needs free intracellular Mg to fall below physiological levels for PLC-dependent inhibition to occur.…”

Section: A Biophysical Description Of the Channel Function Permeatmentioning

confidence: 99%

Trpm7

Fleig

Chubanov

2014

Handbook of Experimental Pharmacology

View full text Add to dashboard Cite

The channel kinases TRPM6 and TRPM7 are fusion proteins with an ion transport domain and an enzymatically active kinase domain. TRPM7 has been found in every mammalian tissue investigated to date. The two-in-one protein structure, the ubiquitous expression profile, and the protein’s unique biophysical characteristics that enable divalent ion transport involve TRPM7 in a plethora of (patho)physiological processes. With its prominent role in cellular and systemic magnesium homeostasis, TRPM7 emerges as a key player in embryonic development, global ischemia, cardiovascular disease, and cancer.

show abstract

Inhibition of the Magnesium-Sensitive TRPM7-like Channel in Cardiac Myocytes by Nonhydrolysable GTP Analogs: Involvement of Phosphoinositide Metabolism

Cited by 18 publications

References 33 publications

Detailed examination of Mg²⁺ and pH sensitivity of human TRPM7 channels

Detailed examination of Mg²⁺ and pH sensitivity of human TRPM7 channels

Sensitivity of TRPM7 channels to Mg²⁺ characterized in cell-free patches of Jurkat T lymphocytes

Trpm7

Contact Info

Product

Resources

About

Inhibition of the Magnesium-Sensitive TRPM7-like Channel in Cardiac Myocytes by Nonhydrolysable GTP Analogs: Involvement of Phosphoinositide Metabolism

Cited by 18 publications

References 33 publications

Detailed examination of Mg2+ and pH sensitivity of human TRPM7 channels

Detailed examination of Mg2+ and pH sensitivity of human TRPM7 channels

Sensitivity of TRPM7 channels to Mg2+ characterized in cell-free patches of Jurkat T lymphocytes

Trpm7

Contact Info

Product

Resources

About

Detailed examination of Mg²⁺ and pH sensitivity of human TRPM7 channels

Detailed examination of Mg²⁺ and pH sensitivity of human TRPM7 channels

Sensitivity of TRPM7 channels to Mg²⁺ characterized in cell-free patches of Jurkat T lymphocytes