Potassium (K+) channels comprise the largest ion channel family with channel structure, function and modulation exhibiting considerable diversity. One particular subfamily, characterised by the presence of two conduction pores and four transmembrane domains (2P/4TM; K2P), generates a leak conductance, which contributes to repolarisation and maintainenance of resting membrane potential. A number of K2P channels are expressed in the human placenta (Bai et al., 2005a) and uterus (Bai et al., (2005b) but there is little information on the tissue distribution of TWIK-2 between the non-pregnant and pregnant state. During pregnancy, paracrine and autocrine interactions maintain the uterus in an electrically inexcitable state in order to promote fetal growth and development. We have studied the tissue distribution of TWIK -2 (Tandem of pore domains in Weak Inward rectifier K+ channels-2), a particular K2P that is expressed in peripheral tissues and is sensitive to internal acidification but insensitive to the classical K+ channel blockers TEA and 4-AP. Myometrial samples and placentae were obtained at elective caesarean section. Placentae were immediately separated into amnion, chorion, decidua and villous constituents. Endometrium and myometrium from non-pregnant, normally cycling women were taken at hysterectomy. All samples were rapidly snap-frozen for western blotting investigations. Patients gave fully informed written consent and the study had local ethics approval. Crude tissue lysates were prepared from uterine and placental tissues following homogenisation and centrifugation. Proteins were then resolved by SDS-PAGE and transferred onto nitrocellulose. After blocking in 7% non-fat milk and washing, membranes were probed using an anti-TWIK-2 antibody (1:250, Alomone Labs, Israel) followed by incubation in alkaline-phosphatase linked secondary antibody and detection by chemiluminescence (Immunstar, BioRad, UK). Our results demonstrate the presence of a 34 kDa band consistent with expression of TWIK 2. Highest expression was observed in non-pregnant and pregnant myometrium with endometrium, decidua, chorion and cytotrophoblast also exhibiting significant amounts. TWIK-2 protein was undetectable in amnion. The presence of large amounts of TWIK-2 in myometrium suggests that it may be important in dampening contractions until labour thereby mediating gestational quiescence. Its presence in other intrauterine tissues may indicate a role for it as a molecular sensor of pH. Studies are underway in order to characterise TWIK-2 function in these tissues.