Inositol 1,4,5-trisphosphate mediates adrenaline activation of K+ conductance in mouse peritoneal macrophages

A potassium ion channel is involved in cytokine production by activated human macrophages

Macrophages play an important role in immune and inflammatory responses, largely through secretion of bioactive molecule such as cytokines. While calcium is known to be an important regulator of this process, less is known about the role of other ions and the ion channels that regulate them. We have previously implicated an outwardly rectifying potassium channel (Kor) in this process and for this reason we have investigated the role of potassium (K+) and K+ channels in the regulation of tumour necrosis factor-alpha (TNF-alpha)and interleukin (IL)-8 production by activated human culture-derived macrophages. The effect of blockade of Kor is to inhibit phorbol myristate acetate (PMA)-induced cytokine production by translational or post-translational mechanisms, an effect that is duplicated by increasing extracellular K+. By contrast, the effects of K+ on LPS-stimulated cells are far more complex and are probably mediated through the change of osmolality and occur largely at the mRNA level. This data directly implicates K+, and its regulation through Kor, in early events following PMA stimulation of these cells.

The alpha 1A-adrenoceptor couples to Ca2+ mobilization in mouse peritoneal macrophages

Activation of the alpha 1-adrenoceptor (alpha 1-AR) in mouse peritoneal macrophages induces a Ca(2+)-dependent K+ current via release of Ca2+ from internal stores [Hara et al. (1991) Pflügers Arch 419: 371-379]. In order to characterize the alpha 1-AR subtype in macrophages, we examined potencies of the alpha 1-AR subtype-selective antagonists against epinephrine-induced increases in intracellular Ca2+ concentration ([Ca2+]i). The Ki values for the alpha 1-AR in macrophages of WB4101, 5-methylurapidil and phentolamine were 0.13 nM, 0.15 nM and 7.0 nM, respectively. (+)-Niguldipine (10 nM) completely blocked the response. Treatment with chloroethylclonidine (CEC) did not abolish the response. These pharmacological properties of the alpha 1-AR in macrophages agree quite well with those of the alpha 1A subtype.