ROMK inward-rectifier K ؉ channels control renal K ؉ secretion. The activity of ROMK is regulated by protein kinase A (PKA), but the molecular mechanism for regulation is unknown. Having found that direct interaction with membrane phosphatidylinositol 4,5-bisphosphate (PIP 2 ) is essential for channel activation, we investigate here the role of PIP 2 in regulation of ROMK1 by PKA. By using adenosine-5-[␥-thio]triphosphate) (ATP[␥S]) as the substrate, we found that PKA does not directly activate ROMK1 channels in membranes that are devoid of PIP 2 . Rather, phosphorylation by PKA ؉ ATP[␥S] lowers the concentration of PIP 2 necessary for activation of the channels. In solution-binding assays, anti-PIP 2 antibodies bind PIP 2 and prevent PIP 2 -channel interaction. In inside-out membrane patches, antibodies inhibit the activity of the channels. PKA treatment then decreases the sensitivity of ROMK1 for inhibition by the antibodies, indicating an enhanced interaction between PIP 2 and the phosphorylated channels. Conversely, mutation of the PKA phosphorylation sites in ROMK1 decreases PIP 2 interaction with the channels. Thus, PKA activates ROMK1 channels by enhancing PIP 2 -channel interaction.Inward-rectifier K ϩ channels more readily conduct current inward than outward. They are widely present and regulate many important cellular processes, including resting membrane potential, cell and synaptic excitability, pancreatic insulin secretion, and renal K ϩ transport (1). Many cDNAs for the inward-rectifier K ϩ channel family have been isolated, including the rat kidney ROMK1, the strongly rectifying IRK1, the G protein-gated GIRK1, and the pancreatic beta cell inward rectifier BIR (2). These cDNAs encode polypeptides of Ϸ300-500 aa, which share Ϸ40% or more amino acid identity and have the common structure of a cytoplasmic N terminus, two hydrophobic segments (M1 and M2) that span the membrane as ␣-helices, one pore-forming partial membrane-spanning region (H5), and a long cytoplasmic C terminus.Opening of the G protein-gated GIRK1/4 channels requires G protein ␤␥ subunits (3, 4). Other inward-rectifier K ϩ channels, such as ROMK1 and IRK1, are constitutively open. Inward-rectifier K ϩ channels run down when inside-out membrane patches are excised into ATP-free, Mg 2ϩ -containing solution. Recent evidence implicates PIP 2 as a regulator of inward-rectifier channels. We and others (5-8) have reported that depletion of membrane PIP 2 causes channel run-down. Direct application of PIP 2 -containing liposomes to the membrane patches reactivates run-down channels, and application of Mg-ATP to membrane patches reproduces the effect by activating membrane-associated lipid kinases (which phosphorylate phosphatidylinositol and phosphatidylinositol 4-phosphate) to generate PIP 2 in situ (9).Phosphorylation by cAMP-dependent protein kinase (PKA) controls the activity of ion channels in many tissues by a variety of mechanisms (10). For example, PKA phosphorylation on the voltage-gated delayed-rectifier K ϩ channels in squ...

OCT4 and SOX2 are biomarkers of tumorigenesis and early stage OSCC. SOX2 is an independent prognostic factor for OSCC.

Our results showed that the three loci, C1236T, G2677T and C3435T, jointly influenced the treatment response for epileptic patients. They should be regarded together as a complex polymorphic drug-response system. These findings suggest that examination of the haplotypes of the three loci could be useful in predicting drug resistance in epilepsy.

Parkinson's disease (PD) is a progressive disease related to degeneration of nigrostriatal dopaminergic neurons and can be caused by genetic and environmental factors. N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can produce Parkinsonian syndrome (Langston et al. 1983) and is an Received February 28, 2010; revised manuscript received April 26, 2010; accepted April 26, 2010. Address correspondence and reprint requests to Kai-Yuan Tzen, MD, Department of Nuclear Medicine, National Taiwan University Hospital, No.7 Chung Shan South Road, Taipei 100, Taiwan. E-mail: tzenky@ntuh.gov.tw or Chun-Jung Lin, School of Pharmacy, College of Medicine, National Taiwan University,1 Jen-Ai Road, Section 1, Taipei, Taiwan 100. E-mail: clementumich@ntu.edu.tw Abbreviations used: 3-MT, 3-methoxytyramine; ARBECs, adult rat brain endothelial cells; AUC, area under the time-concentration curve; BB, blood-brain barrier; BMECs, brain microvessel endothelial cells; BSA, bovine serum albumin; DC, detergent compatible; DOPAC, 3,4-dihydroxyphenylacetic acid; ECF, extracellular fluid; FDOPA, 6-[ AbstractThe cellular localization of organic cation transporter (OCT) 1 and OCT2 in isolated brain microvessel endothelial cells from humans, rats, and mice and in cultured adult rat brain endothelial cells was examined by confocal microscopy and in isolated luminal and abluminal membrane fractions by Western blot analysis. Cellular uptake of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was measured with or without OCT1/OCT2 silencing. The interaction between MPTP and amantadine was studied by in vitro kinetic analysis and in vivo brain microdialysis. MPTP-induced dopaminergic toxicity was examined by measuring dopamine levels in the brain striatum and by positron emission tomography scanning. The results showed that both OCT1 and OCT2 were mainly expressed on the luminal side of brain microvessel endothelial cells and adult rat brain endothelial cells. Cellular uptake of MPTP was significantly (p < 0.05) decreased by about 53%, 60%, or 91% following silencing of OCT1, OCT2, or both, respectively. Amantadine competitively inhibited MPTP uptake in vitro and significantly (p < 0.05) reduced the area under the time-concentration curve for MPTP and MPP + in the brain extracellular fluid in rats and mice by 65-70% and 35-85%, respectively. MPTP-induced dopaminergic toxicity in mice was ameliorated by amantadine without stimulating dopamine turnover. In conclusion, OCT1 and OCT2 are important for MPTP transfer across the blood-brain barrier and amantadine reduces the blood-brain barrier transfer of MPTP and MPTP-induced dopaminergic toxicity in rodents.

ROMK channels are responsible for K؉ secretion in kidney. The activity of ROMK is regulated by intracellular pH (pH i ) with acidification causing channel closure (effective pK a ϳ6.9). Recently, we and others reported that a direct interaction of the channels with phosphatidyl-4,5-bisphosphate (PIP 2 ) is critical for opening of the inwardly rectifying K ؉ channels. Here, we investigate the relationship between the mechanisms for regulation of ROMK by PIP 2 and by pH i . We find that disruption of PIP 2 -ROMK1 interaction not only decreases single-channel open probability (P o ) but gives rise to a ROMK1 subconductance state. This state has an increased sensitivity to intracellular protons (effective pK a shifted to pH ϳ7.8), such that the subconductance channels are relatively quiescent at physiological pH i . Open probability for the subconductance channels can then be increased by intracellular alkalinization to supra-physiological pH. This increase in P o for the subconductance channels by alkalinization is not associated with an increase in PIP 2 -channel interaction. Thus, direct interaction with PIP 2 is critical for ROMK1 to open at full conductance. Disruption of this interaction increases pH i sensitivity for the channels via emergence of the subconductance state. The control of open probability of ROMK1 by pH i occurs via a mechanism distinct from the regulation by PIP 2 .Potassium channels play important roles in the regulation of potassium transport in kidney (1). Recently, cDNAs for the renal K ϩ channels and splice isoforms, ROMK1, -2, and -3, have been isolated (2-4). ROMKs belong to a large family of inward rectifier K ϩ channels, which also includes the strongly rectifying IRK1, the G protein-gated GIRK1, and the pancreatic ␤-cell inward rectifier (5). These cDNAs encode polypeptides of ϳ300 -500 amino acids, which share ϳ40% or more amino acid identity and have the common structure of a cytoplasmic N terminus, two hydrophobic segments that span the membrane as ␣-helices, one pore-forming partial membranespanning region, and a long cytoplasmic C terminus.Opening of the G protein-gated GIRK channels requires G protein ␤␥ subunits. Other inward rectifier K ϩ channels, such as ROMK1 and IRK1, are constitutively open (5). Inward rectifier K ϩ channels run down (close) when inside-out membrane patches are excised into ATP-free, Mg 2ϩ -containing solution. We and others (6 -9) recently found that direct interaction of inward rectifier channels with the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP 2 ) 1 is critical for channel opening. Reduction of membrane PIP 2 via activation of the Mg 2ϩ -dependent lipid phosphatases causes channel run-down. Direct application of PIP 2 -containing liposomes to membrane patches reactivates run-down channels (6 -9). Furthermore, PIP 2 is important for regulation of the G protein-gated channels by G␤␥ and by intracellular Na ϩ (8 -11) and modulates ATP sensitivity of K ATP channels (12, 13).ROMK1 channels are also regulated by cAMP-dependent protein kina...