Cellular Localization of THIK-1 (K_2P13.1) and THIK-2 (K_2P12.1) K⁺ Channels in the Mammalian Kidney

Abstract

K⁺-channels fulfill several important functions in the mammalian kidney such as volume regulation, recirculation and secretion of K⁺ ions, and maintaining the resting potential. In this study we used immunocytochemical methods, in situ hybridization, and nephron segment-specific RT-PCR to obtain a detailed picture of the cellular localization of two tandem pore domain potassium (K_2P) channels, THIK-1 (K_2P13.1, KCNK13) and THIK-2 (K_2P12.1, KCNK12). Monospecific antibodies against C-terminal domains of rat THIK-1 and THIK-2 proteins (GST-fusion proteins) were raised in rabbits, freed from cross-reactivity, and affinity purified. All antibodies were validated by Western blot analysis, competitive ELISA, and preabsorption experiments. The expression of THIK channels in specific nephron segments was confirmed by double staining with marker proteins. Results indicate that in rat and mouse THIK-1 and THIK-2 were expressed in the proximal tubule (PT), thick ascending limb (TAL), connecting tubule (CNT), and cortical collecting duct (CCD). In human kidney THIK-1 and THIK-2 were localized in PT, TAL and CCD. Immunostaining of rat tissue revealed an intracellular expression of THIK-1 and THIK-2 throughout the identified nephron segments. However in mouse kidney THIK-2 was identified in basolateral membranes. Overall, the glomerulus, thin limbs and medullary collecting ducts were devoid of THIK-1 and THIK-2 signal. In summary, THIK-1 and THIK-2 are abundantly expressed in the proximal and distal nephron of the mammalian kidney.

Tandem Pore Domain Halothane-inhibited K+ Channel Subunits THIK1 and THIK2 Assemble and Form Active Channels

“…Both subunits have the same localization along the mammalian nephron and collecting duct system (31). Only slight differences in intensity and subcellular distribution were observed (31).…”

“…However, overlapping distributions in some tissues suggest in vivo formation of functional heterodimers, for instance in the olfactory bulb or hippocampus of adult rat brain (24) and in mouse, rat, and human kidneys (31). Also, changes in the ratio of THIK1 and THIK2 in some tissues or in certain conditions may also significantly influence assembly and composition of THIK channels.…”

Silencing of the Tandem Pore Domain Halothane-inhibited K+ Channel 2 (THIK2) Relies on Combined Intracellular Retention and Low Intrinsic Activity at the Plasma Membrane

“…Such a regulatory mechanism, by altering the efficiency of THIK2 channel surface expression, may influence cellular excitability on a more dynamic basis by providing the cells with a pool of releasable channels. Perspectives-THIK1 and THIK2 have different patterns of expression in the kidney and the brain (6,45). In the cerebellum and several specific nuclei (amygdala basolateral nuclei, thalamus ventral posterior nuclei, oculomotor nucleus, and so forth) where THIK1 is not detected, THIK2 is highly expressed (6).…”

Molecular Background of Leak K+Currents: Two-Pore Domain Potassium Channels

“…Human THIK-2 mRNA was most abundant in the heart, skeletal muscle, and pancreas as determined by Northern blot (112). Recently, both THIK-1 and THIK-2 were detected in the kidney, in the same structures where ROMK (K IR 1.1) inwardly rectifying K ϩ channel is also expressed (315).…”