Neurochemistry International 45 (2004) 437–442 Kinin receptors in cultured rat microglia Mami Noda a,∗ , Yukihiro Kariura a , Taiju Amano a , Yoshimasa Manago a , Kaori Nishikawa b , Shunsuke Aoki b , Keiji Wada b a Laboratory of Pathophysiology, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Fukuoka 812-8582, Japan b Department of Degenerative Neurological Diseases, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Kodaira, Tokyo 187-8502, Japan Received 15 May 2003; received in revised form 29 July 2003; accepted 29 July 2003 Abstract Kinins are produced and act at the site of injury and inflammation in various tissues. They are likely to initiate a particular cascade of inflammatory events, which evokes physiological and pathophysiological responses including an increase in blood flow and plasma leakage. In the central nervous system (CNS), kinins are potent stimulators of the production and release of pro-inflammatory mediators represented by prostanoids and cytotoxins. They are known to induce neural tissue damage. Many of the cytotoxins such as cytokines and free radicals and prostanoids are released from glial cells. Among glial cells, astrocytes and oligodendrocytes are known to possess bradykinin (BK) B 2 receptors that phosphoinositide (PI) turnover and raise intracellular Ca 2+ concentration. The presence of bradykinin receptors in microglia has been of great significance. We recently showed that rat primary microglia express kinin receptors. In resting microglia, B 2 receptors but not B 1 receptors are expressed. When the microglia are activated by bradykinin, B 1 receptors are up-regulated, while B 2 receptors are down-regulated. As observed in other glial cells, electrophysiological measurements suggest that B 2 receptors in phosphoinositide turnover and intracellular Ca 2+ concentration in microglia. Release of cytotoxins is likely consequent upon the activation of BK receptors. Our study provides the first evidence that microglia express functional kinin receptors and suggests that microglia play an important role in CNS inflammatory responses. © 2004 Elsevier Ltd. All rights reserved. Keywords: Bradykinin; Signal transduction; RT-PCR; Patch-clamp; K + currents 1. Introduction The nonapeptide, bradykinin (BK), a mediator of inflam- mation and a vasodepressor, is produced in the brain during trauma and stroke, and is thought to open the blood–brain barrier. There are two subtypes of BK receptor, B 1 and B 2 , which have been pharmacologically defined using a variety of peptidergic agonists and antagonists (Hall, 1992). The B 2 receptor is constitutively expressed in various mammalian tissues, while the B 1 receptor subtype is believed to be expressed at very low levels under normal conditions but is up-regulated by treatment with lipopolysaccharide (LPS) or cytokines such as interleukin-1 (IL-1). The B 2 receptor was cloned from the rat using a Xeno- pus oocyte assay (McEachern et al., 1991). Consequently, the cDNA (Hess et al., 1992) and genomic human DNA (Eggerickx et al., 1992; Kammerer et al., 1995) of the B 2 receptor were cloned and localized to chromosome 14q32 ∗ Corresponding author. Tel.: +81-92-642-6574; fax: +81-92-642-6574. E-mail address: noda@phar.kyushu-u.ac.jp (M. Noda). (Powell et al., 1993; Ma et al., 1994a). The rabbit, pig, mouse, rat, and canine B 2 receptors were also identified (McIntyre et al., 1993; Hess et al., 1994, 2001; Ma et al., 1994b; Bachvarov et al., 1995; Farmer et al., 1998; Ni et al., 1998a). The deduced amino acid sequences of the B 2 recep- tors from all species share extensive homology with ∼80%. The B 1 receptor was cloned first in human (Menke et al., 1994), then in rabbit (MacNeil et al., 1995), mice (Pesquero et al., 1996) and rats (Ni et al., 1998b). The human B 1 re- ceptor has 36% homology in amino acid sequence to human B 2 receptor. The BK receptors belong to the family of receptors with seven transmembrane domains coupled to G-proteins (Gi and Gq/11) and mediate a number of biochemical sig- nals via the second messenger system (Fig. 1). Actually, immunoprecipitation of photoaffinity-labeled G-proteins demonstrated that both B 1 and B 2 receptor are coupled to Gq and Gi subunits (Austin et al., 1997; de Weerd and Leeb-Lundberg, 1997). Some members of the Gq family is involved in phosphoinositide (PI) turnover. In addition, the G dimer, dissociated from activated Gi-protein 0197-0186/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuint.2003.07.007