The inward rectifier potassium channel Kir2.1 is expressed in mouse neutrophils from bone marrow and liver

Abstract

Neutrophils are phagocytic cells that play a critical role in innate immunity by destroying bacterial pathogens. Channels belonging to the inward rectifier potassium channel subfamily 2 (Kir2 channels) have been described in other phagocytes (monocytes/macrophages and eosinophils) and in hematopoietic precursors of phagocytes. Their physiological function in these cells remains unclear, but some evidence suggests a role in growth factor-dependent proliferation and development. Expression of functional Kir2 channels has not been definitively demonstrated in mammalian neutrophils. Here, we show by RT-PCR that neutrophils from mouse bone marrow and liver express mRNA for the Kir2 subunit Kir2.1 but not for other subunits (Kir2.2, Kir2.3, and Kir2.4). In electrophysiological experiments, resting (unstimulated) neutrophils from mouse bone marrow and liver exhibit a constitutively active, external K+-dependent, strong inwardly rectifying current that constitutes the dominant current. The reversal potential is dependent on the external K+ concentration in a Nernstian fashion, as expected for a K+-selective current. The current is not altered by changes in external or internal pH, and it is blocked by Ba2+, Cs+, and the Kir2-selective inhibitor ML133. The single-channel conductance is in agreement with previously reported values for Kir2.1 channels. These properties are characteristic of homomeric Kir2.1 channels. Current density in short-term cultures of bone marrow neutrophils is decreased in the absence of growth factors that are important for neutrophil proliferation [granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF)]. These results demonstrate that mouse neutrophils express functional Kir2.1 channels and suggest that these channels may be important for neutrophil function, possibly in a growth factor-dependent manner.

Expression and contributions of the Kir2.1 inward-rectifier K+ channel to proliferation, migration and chemotaxis of microglia in unstimulated and anti-inflammatory states

“…Finally, a dose-response curve for ML133 block was constructed and yielded an IC 50 of 3.5 μM ( n = 4–7 cells for each point, Figure 1F ). This value is comparable to the reported values in HEK cells (Wang et al, 2011 ) and murine neutrophils (Masia et al, 2015 ).…”

“…ML133 is a recently identified small molecule inhibitor of the Kir2-family, and it blocks Kir2.1 heterologously expressed in HEK cells with an IC 50 of 1.8 μM at 7.4 pH (less effective at lower pH; Wang et al, 2011 ). Very few studies have used ML133 (Wang et al, 2011 ; Masia et al, 2015 ), and it has not been reported for microglia.…”

Quantitative in vivo imaging of neuronal glucose concentrations with a genetically encoded fluorescence lifetime sensor

“…For this, we designed an extracellular solution that mimics the ionic composition of the cytosol, and causes minimal interference with the expected behavior of the sensor. The solution where glucose was applied contained physiological concentrations of K + , Na + and Cl − (Alberts et al, ), along with gluconate as the major anion (Lutas, Birnbaumer, & Yellen, ; Masia, Krause, & Yellen, ). Free Mg 2+ concentration was adjusted within the range of physiological values (Romani & Scarpa, ) and free Ca 2+ was buffered at ~80 nM, which is close to the Ca 2+ concentration at rest in HEK293 cells (Tong, McCarthy, & MacLennan, ), and neurons (Grienberger & Konnerth, ).…”

“…, along with gluconate as the major anion (Lutas, Birnbaumer, & Yellen, 2014;Masia, Krause, & Yellen, 2015). Free Mg 2+ concentration was adjusted within the range of physiological values (Romani & Scarpa, 1992) and free Ca 2+ was buffered at ~80 nM, which is close to the Ca 2+ concentration at rest in HEK293 cells (Tong, McCarthy, & MacLennan, 1999), and neurons (Grienberger & Konnerth, 2012).…”

The K + channel K IR 2.1 functions in tandem with proton influx to mediate sour taste transduction

“…Sensitivity to intracellular acidification is not a well-documented feature of K IR 2.1 as it is for other K IR and K 2P channels (35,36). We therefore tested whether heterologously expressed K IR 2.1 channels could be blocked by intracellular acidification.…”