Corticotropin Induces the Expression of TREK-1 mRNA and K⁺Current in Adrenocortical Cells

Abstract

Bovine adrenal zona fasciculata (AZF) cells express a two-pore/ four-transmembrane segment bTREK-1 K ϩ channel that sets the resting potential and couples hormonal signals to depolarizationdependent Ca 2ϩ entry and cortisol secretion. It was discovered that corticotropin (1-2000 pM) enhances the expression of bTREK-1 mRNA and membrane current in cultured AZF cells. Forskolin and 8-pcpt-cAMP mimicked corticotropin induction of bTREK-1 mRNA, but angiotensin II (AII) was ineffective. The induction of bTREK-1 mRNA by corticotropin was partially blocked by the A-kinase antagonist H-89. 8-(4-Chloro-phenylthio)-2-Omethyladenosine-3Ј-5Ј-cyclic monophosphate, a cAMP analog that activates cAMP-regulated guanine nucleotide exchange factors (Epac), failed to increase bTREK-1 mRNA. Corticotropinstimulated increases in bTREK-1 mRNA were eliminated by inhibitors of protein synthesis or gene transcription. bTREK-1 current disappeared after 24 h in serum-supplemented medium, but in the presence of corticotropin, bTREK-1 expression was maintained for at least 48 h. The enhancement of bTREK-1 mRNA and ionic current contrasts with the corticotropin-induced down-regulation of the Kv1.4 voltage-gated K ϩ current and associated mRNA in AZF cells. These results demonstrate that corticotropin rapidly and potently induces the expression of bTREK-1 in AZF cells at the pretranslational level by a cAMP-dependent mechanism that is partially dependent on A-kinase but independent of Epac and Ca 2ϩ . They further indicate that prolonged stimulation of AZF cells by corticotropin, as occurs during long-term stress or disease, may produce pronounced changes in the expression of genes encoding ion channels, thereby reshaping the electrical properties of these cells to enhance or limit cortisol secretion.Although cortisol-secreting cells of the adrenal zona fasciculata (AZF) lack Na ϩ -dependent action potentials, a hallmark of excitable cells, ion channels play a prominent role in the physiology of cortisol secretion (Enyeart et al., , 1996bMlinar et al., 1993a). AZF cells express both voltagegated Ca 2ϩ and K ϩ channels and maintain resting membrane potentials near the K ϩ equilibrium potential (Mlinar et al., 1993a,b;Mlinar and Enyeart, 1993). Corticotropin-and AII-stimulated cortisol secretion by AZF cells involves depolarization-dependent Ca 2ϩ entry through Ca 2ϩ channels Mlinar et al., 1993a,b).Ion channels in adrenal cortical cells have been identified and characterized using a combination of patch clamp and molecular methods. In addition to low voltage-activated Ttype Ca 2ϩ channels, bovine AZF cells express two types of K ϩ -selective channels. These include a voltage-gated, rapidly inactivating Kv1.4 K ϩ channel and a noninactivating, background K ϩ channel (Mlinar et al., 1993a;Mlinar and Enyeart, 1993;Enyeart et al., 2002). Recently, we identified the background channel as bTREK-1 (or KCNK2), a member of the two-pore, four-transmembrane-segment (2P/4TMS) family of K ϩ channels (Fink et al., 1996;Maingret et al., 2000;Goldstein...

Adrenal fasciculata cells express T-type and rapidly and slowly activating L-type Ca2+ channels that regulate cortisol secretion

“…Total RNA isolation and Northern blot procedures are described elsewhere (12). Briefly, 5-7 ϫ 10 6 AZF cells were plated on 60-mm fibronectintreated dishes in DMEM/F-12ϩ.…”

Deafness associated changes in expression of two-pore domain potassium channels in the rat cochlear nucleus

“…The expression of two-pore domain K + channels has been shown to be influenced by activity as well as biochemical and physical cues (Enyeart et al, 2003;Kang et al, 2004;Li et al, 2005;Liu and Saint, 2004;Xu et al, 2004;Yeom et al, 2005). Therefore, these channels may play a role in synaptic plasticity, where activity-dependent signaling can alter the inherent excitability of target neurons.…”

Deafness associated changes in two-pore domain potassium channels in the rat inferior colliculus

“…The expression of K 2p channels can be regulated by biochemical and physical cues as well as activity (Enyeart et al, 2003;Holt et al, 2006;Kang et al, 2004;Li et al, 2005;Liu and Saint, 2004;Xu et al, 2004 andYeom et al, 2005). These channels could play a role in activitydependent synaptic plasticity, where intracellular signaling induced by changes in activity level can alter the properties of target neurons.…”