TREK-1 currents in smooth muscle cells from pregnant human myometrium

Abstract

The mechanisms governing maintenance of quiescence during pregnancy remain largely unknown. The current study characterizes a stretch-activated, tetraethylammoniuminsensitive K ϩ current in smooth muscle cells isolated from pregnant human myometrium. This study hypothesizes that these K ϩ currents can be attributed to TREK-1 and that upregulation of this channel during pregnancy assists with the maintenance of a negative cell membrane potential, conceivably contributing to uterine quiescence until full term. The results of this study demonstrate that, in pregnant human myometrial cells, outward currents at 80 mV increased from 4.8 Ϯ 1.5 to 19.4 Ϯ 7.5 pA/pF and from 3.0 Ϯ 0.8 to 11.8 Ϯ 2.7 pA/pF with application of arachidonic acid (AA) and NaHCO 3, respectively, causing intracellular acidification. Similarly, outward currents were inhibited following application of 10 M fluphenazine by 51.2 Ϯ 9.8% after activation by AA and by 73.9 Ϯ 4.2% after activation by NaHCO3. In human embryonic kidney (HEK-293) cells stably expressing TREK-1, outward currents at 80 mV increased from 91.0 Ϯ 23.8 to 247.5 Ϯ 73.3 pA/pF and from 34.8 Ϯ 8.9 to 218.6 Ϯ 45.0 pA/pF with application of AA and NaHCO3, respectively. Correspondingly, outward currents were inhibited 89.5 Ϯ 2.3% by 10 M fluphenazine following activation by AA and by 91.6 Ϯ 3.4% following activation by NaHCO3. Moreover, currents in human myometrial cells were activated by stretch and were reduced by transfection with small interfering RNA or extracellular acidification. Understanding gestational regulation of expression and gating of TREK-1 channels could be important in determining appropriate maintenance of uterine quiescence during pregnancy.

Temperature Sensitivity of Two-Pore (K2P) Potassium Channels

“…While temperature properties of K 2P channels in native and heterologous systems may differ, it is worth noting that since temperature changes produce the most significant effect precisely at T 1/2 , the heat-activated K 2P s are uniquely positioned to sense minute variations of body temperature. In this regard, it is interesting to consider the contribution of heat-evoked potassium current to the physiology of cells and tissues where TREK-1 or other K 2P s have been shown to play functional roles, such as in lung epithelial cells (Davis & Cowley, 2006; Roan, Waters, Teng, Ghosh, & Schwingshackl, 2014; Schwingshackl, Teng, Ghosh, & Waters, 2013), myometrium (Heyman et al, 2013; Wu, Singer, & Buxton, 2012), and endothelium of blood vessels (Bittner et al, 2013; Garry et al, 2007; Namiranian et al, 2010). …”

“…The K 2P s have a nonconventional topology: a mature channel is formed by two subunits, each containing two nonidentical pore-forming domains arranged in tandem (Figure 5.1). The K 2P channels of the TREK/TRAAK group, which includes TREK-1 (K 2P 2.1, KCNK2 ), TREK-2 (K 2P 10.1, KCNK10 ), and TRAAK (K 2P 4.1, KCNK4 ), are expressed in various cell types, including neurons (Acosta et al, 2014; Fink et al, 1996; Kang & Kim, 2006; de la Pena et al, 2012; Talley, Solorzano, Lei, Kim, & Bayliss, 2001), cardiomyocytes (Xian Tao et al, 2006), and arterial myocytes (Bryan et al, 2006; Garry et al, 2007; Heyman et al, 2013). Temperature (Kang, Choe, & Kim, 2005; Maingret et al, 2000), mechanical force (Patel et al, 1998), general anesthetics (Patel et al, 1999), polyunsaturated fatty acids (Patel et al, 1998), and other compounds (Noel, Sandoz, & Lesage, 2011) potentiate the TREK/TRAAK-dependent background potassium efflux and suppress cellular excitability (Acosta et al, 2014; Dey et al, 2014).…”

Prolonged stretching in the late-late pregnant rat uterus inhibits contractions through potassium channel TREK-1

“…Potassium channel TREK-1 is a type of CAP, and have been found to be expressed in the human and rat myometrium, particularly during pregnancy [16]. Based on the topology of the K + channel subunits, these TREK K2P channels are thought to maintain background outward K + current and resting membrane potential and counterbalance membrane depolarization and muscle contractions during pregnancy [17].…”

Progress in understanding electro-mechanical signalling in the myometrium

“…, Heyman et al . ) which was specifically inhibited by reagents that block TREK‐1 channels, such as fluphenazine and L‐methionine. It is clearly tempting to speculate that these channels will contribute to the maintenance of pregnancy as the chronic distension of the myometrial cells stimulates TREK‐1, produces outward current and stabilizes membrane potential away from the threshold for L‐type Ca channels to open.…”

“…Of the two-pore family, several groups have identified TREK-1 (Kcnk2), as being highly expressed in myometrium and regulated during pregnancy and labour (Buxton et al 2010, Monaghan et al 2011. In mouse and human myocytes, TREK-1 channels were activated by stretch (negative pressure in patch pipette) and caused an increase in outward current (Monaghan et al 2011, Heyman et al 2013) which was specifically inhibited by reagents that block TREK-1 channels, such as fluphenazine and L-methionine. It is clearly tempting to speculate that these channels will contribute to the maintenance of pregnancy as the chronic distension of the myometrial cells stimulates TREK-1, produces outward current and stabilizes membrane potential away from the threshold for L-type Ca channels to open.…”