Development of a delayed outward-rectifying K+ conductance in cultured mouse peritoneal macrophages.

Abstract

Patch clamp techniques were used to study ionic currents in cultured mouse peritoneal macrophages. Whole-cell voltage clamp studies of cells 1-5 hr after isolation showed only a high-resistance linear membrane. After 1 day in culture, 82 of 85 cells studied had developed a voltage-and time-dependent potassium (K+) conductance similar to the delayed outward rectifier in nerve and muscle cells. The current activated when the membrane was depolarized above -50 mV. The sigmoidally rising current rose to a peak at a rate that increased with depolarization. Inactivation proceeded exponentially with a time constant of -450 ms. Recovery from inactivation was slow (r = 12 s). The reversal potentials for varying extracellular K+ concentrations followed the Nernst predictions for a KV-specific channel. The conductance was blocked by extracellular 4-aminopyridine and by intracellular tetraethylammonium chloride, barium, and cesium. Singlechannel K+ currents comprising this net current had a conductance of 16 pS, exhibited bursting behavior, and inactivated with time. No inward currents were ever detected in macrophages cultivated for up to 4 days. Short-term exposure to chemoattractant and transmitter agents failed to activate an inward current. Macrophages may change their membrane electrophysiological properties depending on their state of functional activation. We postulate that the K+ conductance develops prior to depolarizing conductances involved in the macrophage's immunological functions.Ionic membrane currents in macrophages may serve as signals between membrane-ligand interactions and cellular reactions such as phagocytosis of microorganisms. Cultured macrophages derived from human monocytes have an excitable membrane (1) and changes in membrane potential are among the earliest detectable events upon stimulation of phagocytosis (2). So far, direct membrane potential or current measurements have been made with the use of intracellular glass microelectrodes (1,3,4). This type of electrode, however, seriously hampers the study of ionic currents in small cells such as macrophages (3). Therefore, we have applied the patch clamp technique (5), which allows high resolution of ionic currents in small cells (diameter, <20 jtm) up to high frequencies (<10 kHz). We report here that on the first day after isolation, mouse peritoneal macrophages develop an outward-rectifying potassium (Kt) conductance, similar to the delayed rectifier in nerve (6-8) and skeletal muscle membranes (9). The single channels underlying this conductance exhibit a linear current-to-voltage relationship and have a conductance of about 16 pS. Since Nat or Ca2t currents could not be detected in these cells up to 4 days after isolation, we suggest that this conductance is the first conductance expressed in the development of macrophage excitability. MATERIALS AND METHODSResident macrophages were isolated from the peritoneal cavity of male NMRI mice of 20-22 g (Charles River Wiga GmbH, Sulzfeld, Federal Republic of Germany) as described elsewhere ...

Modulation of Voltage-Dependent and Inward Rectifier Potassium Channels by 15-Epi-Lipoxin-A4 in Activated Murine Macrophages: Implications in Innate Immunity

“…Indeed, blockade of K v 1.3 suppresses Ag-driven proliferation and cytokine production in T cells, and selective K v 1.3 blockers ameliorate experimental allergic encephalomyelitis in rats induced by the adoptive transfer of myelin-specific activated effector memory T cells (39)(40)(41)(42). Moreover, several groups have reported the expression of K v 1.3 in macrophages and microglia (5,16,(43)(44)(45)(46)(47)(48), and our data add new insights on the fine-tuning of these channels by lipoxins. Indeed, K v 1.3 channels, together with K ir 2.1, K v 1.5, K Ca 3.1, and BK Ca channels, modulate macrophage and microglia function, and, at the same time, pharmacological channel blockers may have effects on the immune response (5,44,49,50).…”

Modulation of P2X7 nucleotide receptor expression by pro- and anti-inflammatory stimuli in THP-1 monocytes

“…Finally, differentiation of THP-1 cells toward a macrophage phenotype by PMA did not stimulate receptor expression. Monocyte/macrophage activation modulates the expression of other membrane channels, including the outwardly rectifying potassium channels [29,30] and the L-arginine transporter [31]. To date the P2X 7 R is the only ligand-gated channel known to be induced during monocyte/macrophage activation.…”

Mitogen induction of ion channels in murine T lymphocytes.

“…The expression of ion channels in murine macrophages varies markedly at different times after plating of suspended cells (Ypey and Clapham, 1984;Gallin and Sheehy, 1985); this is possibly related to the activation of these cells during the process of adherence to the substrate . To test whether in vitro cell culture might alter the expression of ion channels in murine T cells, we compared MRL-41 0 THE JOURNAL OF GENERAL PHYSIOLOGY -VOLUME 89 " 1987 n cells cultured for l, 2, or 3 d after separation .…”

“…We designated the two types of K+ channels type l (for lpr, or "large") and type n ("normal") . Type n K+ channels closely resemble voltage-gated K+ channels in human T cells (DeCoursey et al ., 19846 ;Cahalan et al ., 1985) and in murine macrophages (Ypey and Clapham, 1984 ;Gallin and Sheehy, 1985) . We used several approaches to determine which types of channels were present in individual murine T cells.…”