Opening velocity, a novel parameter, for finger tapping test in patients with Parkinson's disease.

OBJECTIVES: A new system consisting of an accelerometer and touch sensor was developed to find objective parameters for the finger tapping (FT) test in patients with Parkinson's disease (PD). METHODS: We recruited sixteen patients with PD and thirty-two age-matched healthy volunteers (HVs). By using this new system, various parameters related to velocity, amplitude, rhythm and number in the FT test were measured in patients with PD and examined in comparison with those of HVs on the basis of the Unified Parkinson's Disease Rating Scale (UPDRS) FT score. RESULTS: The new system allowed us to measure fourteen parameters of FT movement very easily, and a radar chart showed obvious differences in most of these parameters between HVs and patients with PD. Principal component analysis showed that fourteen parameters were classified into three components: (1) both mean and standard deviation (SD) of both amplitude and velocity, (2) number of FT for 60s and mean FT interval, and (3) SD of FT interval. The first (velocity- and amplitude-related parameters) and third (rhythm-related parameters) components contributed to discrimination of PD from HVs. Maximum opening velocity (MoV) was the best of these parameters because of its sensitivity and association with the UPDRS FT score. CONCLUSIONS: A novel system for the FT test, which is compact, simple and efficient, has been developed. Velocity- and amplitude-related parameters were indicated to be valuable for evaluation of the FT test in patients with PD. In particular, we first propose that MoV is a novel marker for the FT test.

Characterization of a novel ATP-sensitive K+ channel opener, A-251179, on urinary bladder relaxation and cystometric parameters.

BACKGROUND AND PURPOSE: ATP-sensitive K(+) channels (K(ATP)) play a pivotal role in contractility of urinary bladder smooth muscle. This study reports the characterization of 4-methyl-N-(2,2,2-trichloro-1-(3-pyridin-3-ylthioureido)ethyl)benzamide (A-251179) as a K(ATP) channel opener. EXPERIMENTAL APPROACH: Glyburide-sensitive membrane potential, patch clamp and tension assays were employed to study the effect of A-251179 in vitro. The in vivo efficacy of A-251179 was characterized by suppression of spontaneous contractions in obstructed rat bladder and by measuring urodynamic function of urethane-anesthetized rat models. KEY RESULTS: A-251179 was about 4-fold more selective in activating SUR2B-Kir6.2 derived K(ATP) channels compared to those derived from SUR2A-Kir6.2. In pig bladder smooth muscle strips, A-251179 suppressed spontaneous contractions, about 27- and 71-fold more potently compared to suppression of contractions evoked by low-frequency electrical stimulation and carbachol, respectively. In vivo, A-251179 suppressed spontaneous non-voiding bladder contractions from partial outlet-obstructed rats. Interestingly, in the neurogenic model where isovolumetric contractions were measured by continuous transvesical cystometry, A-251179 at a dose of 0.3 micromol kg(-1), but not higher, was found to increase bladder capacity without affecting either the voiding efficiency or changes in mean arterial blood pressure. CONCLUSIONS AND IMPLICATIONS: The thioureabenzamide analog, A-251179 is a potent novel K(ATP) channel opener with selectivity for SUR2B/Kir6.2 containing K(ATP) channels relative to pinacidil. The pharmacological profile of A-251179 is to increase bladder capacity and to prolong the time between voids without affecting voiding efficiency and represents an interesting characteristic to be explored for further investigations of K(ATP) channel openers for the treatment of overactive bladder.

Ca(2+) elevation evoked by membrane depolarization regulates G protein cycle via RGS proteins in the heart.

Regulators of G protein signaling (RGS), which act as GTPase activators, are a family of cytosolic proteins emerging rapidly as an important means of controlling G protein-mediated cell signals. The importance of RGS action has been verified in vitro for various kinds of cell function. Their in situ modes of action in intact cells are, however, poorly understood. Here we show that an increase in intracellular Ca(2+) evoked by membrane depolarization controls the RGS action on G protein activation of muscarinic K(+) (K(G)) channel in the heart. Acetylcholine-induced K(G) current exhibits a slow time-dependent increase during hyperpolarizing voltage steps, referred to as "relaxation." This reflects the relief from the decrease in available K(G) channel number induced by cell depolarization. This phenomenon is abolished when an increase in intracellular Ca(2+) is prevented. It is also abolished when a calmodulin inhibitor or a mutant RGS4 is applied that can bind to calmodulin but that does not accelerate GTPase activity. Therefore, an increase in intracellular Ca(2+) and the resultant formation of Ca(2+)/calmodulin facilitate GTPase activity of RGS and thus decrease the available channel number on depolarization. These results indicate a novel and probably general pathway that Ca(2+)-dependent signaling regulates the G protein cycle via RGS proteins.

[Activation of ATP-sensitive K+ channels by ADP and K+ channel openers: homology model of sulfonylurea receptor carboxyl-termini].

The ATP-sensitive K+ channels (KATP) are composed of Kir6.0 subunits and sulfonylurea receptors (SUR1, 2A and 2B). SUR2A and SUR2B are splice variants and differ only in the C-terminal 42 amino acid residue (C42). SURs are supposed to be the subunit that determines the different response of KATPs to intracellular nucleotides, K+ channel openers and inhibitors. In this study, we report that C42 of SURs plays critical roles in differential activation of various KATPs by ADP and K+ channel openers such as diazoxide and nicorandil. KATPs containing distinct SURs and Kir6.2 were reconstructed on HEK293T cells. Much higher concentrations of ADP were necessary to activate channels which SUR1 or SUR2B. In all KATPs containing different SUR, diazoxide increased the potency of ADP for channel activity without affecting its efficacy. From the electrophysiological data obtained from C-terminal chimeras and point mutants in the second nucleotide binding domain (NBDs), we developed the homology model of each SUR-NBD2 based on the crystallgraphically determined structure of HisP, a member of the ABC protein superfamily. In this model, C42 is located just beneath the Walker A motif of NBD2 and regulates the binding of nucleotide to NBD2 by affecting the 3-D construct of NBD2. This homology model well explains the different response of KATPs to ADP. Based on this model, it will be possible to develop new ligands for KATPs.

Hypercalcemia in patients with oral squamous cell carcinoma.

Humoral hypercalcemia of malignancy (HHM) is one of the most common metabolic complications associated with cancer. A retrospective study of hypercalcemia in patients with squamous cell carcinoma of the oral cavity was undertaken. All patients were periodically monitored for their serum level of calcium (Ca). Hypercalcemia was defined as a serum Ca concentration higher than 11 mg/dl of the correction for serum albumin concentration. The serum levels of parathyroid hormone related protein (PTH-rP) were also measured by radioimmunoassay. Hypercalcemia was detected in ten of 246 patients (4.1%). All ten patients were at an advanced stage of oral squamous cell carcinoma (SCC, Stage IVA, IVB or IVC). In these ten patients, the serum level of PTH-rP was significantly elevated, 238 +/- 91 pmol/l (range, 108-380 pmol/L). The patients with HHM who underwent antihypercalcemic therapy showed reduced Ca levels relating to PTH-rP levels; however, the Ca concentration was temporarily improved after anti-hypercalcemic treatment. The median survival time after diagnosis of HHM was only 55.8 +/- 19.9 days (range, 27-86 days). HHM in oral cancer is likely attributable to PTH-rP, and its occurrence appears to be an ominous prognostic sign.

Distribution and development of CLN2 protein, the late-infantile neuronal ceroid lipofuscinosis gene product.

Expression of the late-infantile neuronal ceroid lipofuscinosis (LINCL) gene (CLN2) protein was investigated by immunoblotting and immunohistochemistry in human brains and visceral organs of control individuals and of patients with neuronal ceroid lipofuscinosis (NCL). Immunoblotting analyses showed reactivity in the cerebrum, liver, kidney, heart and colon of controls, whereas CLN2 protein was not detected in these organs in a LINCL patient. Immunohistochemistry showed that the reactivity of the protein was ubiquitous in extracerebral organs as well as within the CNS, apparently corresponding to widely distributed deposition of lipopigments in LINCL. The expression of CLN2 protein in the cerebral cortex increased with development, and reached adult level after the age of 2. This development of expression seemed to be related to the onset of LINCL at 2-4 years of age. We confirmed no immunoreactivity in two of three patients with LINCL, who were diagnosed clinicopathologically. One case showing combined ultrastructural morphology of fingerprint profiles and curvilinear bodies had intermediate reactivity, suggesting heterogeneity in clinical LINCL. Evaluation of the immunoreactivity of the CLN2 protein may be useful for characterization of a variant form.

Interaction between the RGS domain of RGS4 with G protein alpha subunits mediates the voltage-dependent relaxation of the G protein-gated potassium channel.

1. In native cardiac myocytes, there is a time dependence to the G protein-gated inwardly rectifying K(+) (K(G)) channel current during voltage steps that accelerates as the concentration of acetylcholine is increased. This phenomenon has been called 'relaxation' and is not reproduced in the reconstituted Kir3.1/Kir3.4 channel in Xenopus oocytes. We have shown that RGS4, a regulator of G protein signalling, restores relaxation to the reconstituted Kir3.1/Kir3.4 channel. In this study, we examined the mechanism of this phenomenon by expressing various combinations of membrane receptors, G proteins, Kir3.0 subunits and mutants of RGS4 in Xenopus oocytes. 2. RGS4 restored relaxation to K(G) channels activated by the pertussis toxin (PTX)-sensitive G protein-coupled m(2)-muscarinic receptor but not to those activated by the G(s) protein-coupled beta(2)-adrenergic receptor. 3. RGS4 induced relaxation not only in heteromeric K(G) channels composed of Kir3.1 and Kir3.4 but also in homomeric assemblies of either an active mutant of Kir3.1 (Kir3.1/F137S) or an isoform of Kir3.2 (Kir3.2d). 4. Truncation mutants of RGS4 showed that the RGS domain itself was essential to reproduce the effect of wild-type RGS4 on the K(G) channel. 5. The mutation of residues in the RGS domain which interact with the alpha subunit of the G protein (G(alpha)) impaired the effect of RGS4. 6. This study therefore shows that interaction between the RGS domain and PTX-sensitive G(alpha) subunits mediates the effect of RGS4 on the agonist concentration-dependent relaxation of K(G) channels.

An inwardly rectifying K(+) channel, Kir4.1, expressed in astrocytes surrounds synapses and blood vessels in brain.

Glial cells express inwardly rectifying K(+) (Kir) channels, which play a critical role in the buffering of extracellular K(+). Kir4.1 is the only Kir channel so far shown to be expressed in brain glial cells. We examined the distribution of Kir4.1 in rat brain with a specific antibody. The Kir4.1 immunostaining distributed broadly but not diffusely in the brain. It was strong in some regions such as the glomerular layer of the olfactory bulb, the Bergmann glia in the cerebellum, the ependyma, and pia mater, while little activity was detected in white matter of the corpus callosum or cerebellar peduncle. In the olfactory bulb, Kir4.1 immunoreactivity was detected in a scattered manner in about one-half of the glial fibrillary acidic protein-positive astrocytes. Immunoelectron microscopic examination revealed that Kir4.1 channels were enriched on the processes of astrocytes wrapping synapses and blood vessels. These data suggest that Kir4.1 is expressed in a limited population of brain astrocytes and may play a specific role in the glial K(+)-buffering action.

Genomic structure and insulin-mediated repression of the aquaporin adipose (AQPap), adipose-specific glycerol channel.

Aquaporin adipose (AQPap) is a putative glycerol channel in adipocytes (Kishida, K., Kuriyama, H., Funahashi, T., Shimomura, I., Kihara, S., Ouchi, N., Nishida, M., Nishizawa, H., Matsuda, M., Takahashi, M., Hotta, K., Nakamura, T., Yamashita, S., Tochino, Y., and Matsuzawa, Y. (2000) J. Biol. Chem. 275, 20896-20902). In the current study, we examined the genomic structure of the mouse AQPap gene and its regulation by insulin. The mouse AQPap gene spanned 12 kilobase pairs in chromosome 4 and consisted of 8 exons and 7 introns. The first two exons, designated exon 1 and exon 1', are alternatively spliced to common exon 2, and thus the AQPap gene possessed two potential promoters. The exon 1-derived transcript is dominant in both adipose tissues and adipocytes on the basis of RNase protection assay and promoter analysis. The mRNA increased after fasting and decreased with refeeding. Insulin deficiency generated by streptozotocin enhanced the mRNA in adipose tissue. Insulin down-regulated AQPap mRNA in 3T3-L1 adipocytes. The AQPap promoter contained heptanucleotide sequences, TGTTTTT at -443/-437, similar to the insulin-response element identified previously in the promoters of insulin-repressed genes. Deletion and single base pair substitution analysis of the promoter revealed that these sequences were required for insulin-mediated repression of AQPap gene transcription. The phosphatidylinositol 3-kinase pathway was involved in this inhibition. We conclude that insulin represses the transcription of AQPap gene via insulin response element in its promoter. Sustained up-regulation of AQPap mRNA in adipose tissue in the insulin-resistant condition may disturb glucose homeostasis by increasing plasma glycerol.

Overexpression of monomeric and multimeric GIRK4 subunits in rat atrial myocytes removes fast desensitization and reduces inward rectification of muscarinic K(+) current (I(K(ACh))). Evidence for functional homomeric GIRK4 channels.

K(+) channels composed of G-protein-coupled inwardly rectifying K(+) channel (GIRK) (Kir3.0) subunits are expressed in cardiac, neuronal, and various endocrine tissues. They are involved in inhibiting excitability and contribute to regulating important physiological functions such as cardiac frequency and secretion of hormones. The functional cardiac (K((ACh))) channel activated by G(i)/G(o)-coupled receptors such as muscarinic M(2) or purinergic A(1) receptors is supposed to be composed of the subunits GIRK1 and GIRK4 in a heterotetrameric (2:2) fashion. In the present study, we have manipulated the subunit composition of the K((ACh)) channels in cultured atrial myocytes from hearts of adult rats by transient transfection of vectors encoding for GIRK1 or GIRK4 subunits or GIRK4 concatemeric constructs and investigated the effects on properties of macroscopic I(K(ACh)). Transfection with a GIRK1 vector did not cause any measurable effect on properties of I(K(ACh)), whereas transfection with a GIRK4 vector resulted in a complete loss in desensitization, a reduction of inward rectification, and a slowing of activation. Transfection of myocytes with a construct encoding for a concatemeric GIRK4(2) subunit had similar effects on desensitization and inward rectification. Following transfection of a tetrameric construct (GIRK4(4)), these changes in properties of I(K(ACh)) were still observed but were less pronounced. Heterologous expression in Chinese hamster ovary cells and human embryonic kidney 293 cells of monomeric, dimeric, and tetrameric GIRK4 resulted in robust currents activated by co-expressed A(1) and M(2) receptors, respectively. These data provide strong evidence that homomeric GIRK4 complexes form functional G(beta)gamma gated ion channels and that kinetic properties of GIRK channels, such as activation rate, desensitization, and inward rectification, depend on subunit composition.

Functional Kir7.1 channels localized at the root of apical processes in rat retinal pigment epithelium.

1. The inwardly rectifying K+ channel current (IK(IR)) recorded from isolated retinal pigmented epithelial (RPE) cells showed poor dependence on external K+ ([K+]o) and low sensitivity to block by Ba2+. We examined the molecular identity and specific subcellular localization of the KIR channel in RPE cells. 2. The Kir7.1 channel current heterologously expressed in HEK293T cells (human embryonic kidney cell line) showed identical properties to those of the RPE IK(IR), i.e. poor dependence on [K+]o and low sensitivity to Ba2+ block. 3. Expression of Kir7.1 mRNA and protein was detected in RPE cells by RT-PCR and immunoblot techniques, respectively. 4. Immunohistochemical studies including electron microscopy revealed that the Kir7.1 channel was localized specifically at the proximal roots of the apical processes of RPE cells, where Na+,K+-ATPase immunoreactivity was also detected. 5. The middle-distal portions of apical processes of RPE cells in the intact tissue exhibited immunoreactivity of Kir4.1, a common KIR channel. In the isolated RPE cells, however, Kir4.1 immunoreactivity was largely lost, while Kir7.1 immunoreactivity remained. 6. These data indicate that the only IK(IR) recorded in isolated RPE cells is derived from the functional Kir7.1 channel localized at the root of apical processes. Co-localization with Na+,K+-ATPase suggests that the Kir7.1 channel may provide the pathway for recycling of K+ to maintain pump activity and thus is essential for K+ handling in RPE cells.

C-terminal tails of sulfonylurea receptors control ADP-induced activation and diazoxide modulation of ATP-sensitive K(+) channels.

The ATP-sensitive K(+) (K(ATP)) channels are composed of the pore-forming K(+) channel Kir6.0 and different sulfonylurea receptors (SURs). SUR1, SUR2A, and SUR2B are sulfonylurea receptors that are characteristic for pancreatic, cardiac, and vascular smooth muscle-type K(ATP) channels, respectively. The structural elements of SURs that are responsible for their different characteristics have not been entirely determined. Here we report that the 42 amino acid segment at the C-terminal tail of SURs plays a critical role in the differential activation of different SUR-K(ATP) channels by ADP and diazoxide. In inside-out patches of human embryonic kidney 293T cells coexpressing distinct SURs and Kir6.2, much higher concentrations of ADP were needed to activate channels that contained SUR2A than SUR1 or SUR2B. In all types of K(ATP) channels, diazoxide increased potency but not efficacy of ADP to evoke channel activation. Replacement of the C-terminal segment of SUR1 with that of SUR2A inhibited ADP-mediated channel activation and reduced diazoxide modulation. Point mutations of the second nucleotide-binding domains (NBD2) of SUR1 and SUR2B, which would prevent ADP binding or ATP hydrolysis, showed similar effects. It is therefore suggested that the C-terminal segment of SUR2A possesses an inhibitory effect on NBD2-mediated ADP-induced channel activation, which underlies the differential effects of ADP and diazoxide on K(ATP) channels containing different SURs.

A regulator of G protein signalling (RGS) protein confers agonist-dependent relaxation gating to a G protein-gated K+ channel.

1. The effects of RGS4 on the voltage-dependent relaxation of G protein-gated K+ (KG) channels were examined by heterologous expression in Xenopus oocytes. 2. While the relaxation kinetics was unaffected by the acetylcholine concentration ([ACh]) in the absence of RGS4, it became dependent on [ACh] when RGS4 was co-expressed. 3. Kinetic analyses indicated that RGS4 confers to the KG channel a voltage-independent inhibitory gating mechanism, which was attenuated by ACh in a concentration-dependent fashion. 4. In vitro biochemical studies showed that RGS4 could bind to the protein complex containing KG channel subunits. 5. Since the native cardiac KG channel exhibited similar agonist-dependent relaxation kinetics to that mediated by RGS4, it is suggested that KG channel gating is a novel physiological target of RGS protein-mediated regulation.

In vivo formation of a proton-sensitive K+ channel by heteromeric subunit assembly of Kir5.1 with Kir4.1.

Kir5.1 is an inwardly rectifying K+ channel (Kir) subunit, whose physiological function is unknown. Human embryonic kidney HEK293T cells co-transfected with rat Kir5.1 and Kir4.1 cDNA expressed a functional K+ channel, whose properties were significantly different from those of the homomeric Kir4.1 channel. Formation of a Kir4. 1/Kir5.1 assembly in HEK293T was confirmed biochemically. We found that heteromeric Kir4.1/Kir5.1 channel activity was affected by internal pH levels between 6.0 and 8.0, when the homomeric Kir4.1 channel activity was relatively stable. Changing external pH in this range had no effect on either Kir channel. Western blot analysis using specific antibodies revealed that Kir4.1 and Kir5.1 proteins were expressed in kidney and brain, but co-immunoprecipitated only from kidney. These results indicate that the co-assembly of Kir5.1 with Kir4.1 occurs in vivo, at least in kidney. The heteromeric Kir4. 1/Kir5.1 channel may therefore sense intracellular pH in renal epithelium and be involved in the regulation of acid-base homeostasis.

Inhibitory effects of vesnarinone on cloned cardiac delayed rectifier K(+) channels expressed in a mammalian cell line.

Vesnarinone, a phosphodiesterase inhibitor, prolongs cardiac action potential duration by inhibiting the delayed rectifier K(+) current, I(K). We examined the effect of this agent on human ether-a-go-go related gene (HERG) and KvLQT1/minK K(+) channels heterologously expressed in human embryonic kidney 293T cells with the whole-cell patch-clamp technique. HERG channel current was inhibited by vesnarinone in a concentration-dependent manner, whereas KvLQT1/minK current was hardly affected by the drug. The inhibition of HERG current by vesnarinone became more prominent and faster as the membrane potential was more depolarized. The properties of inhibition could be described by a first order reaction between the drug and the channel that was apparently independent of HERG channel gating. Although the unbinding rate constant of the drug was constant, the apparent binding rate constant increased as the membrane was more depolarized and the drug concentration was raised. This model also could explain the fast recovery from the drug's effect at hyperpolarized potentials and its rate-dependent inhibition of HERG. Therefore, the effect of vesnarinone on the HERG-K(+) current could be adequately described by a simple kinetic model of drug-channel interaction.

Rapid immunologic diagnosis of classic late infantile neuronal ceroid lipofuscinosis.

OBJECTIVE: To establish a new method for rapid diagnosis of late infantile neuronal ceroid lipofuscinosis (LINCL, CLN2) using specific polyclonal antibodies against the CLN2 gene product. METHODS: Cells and tissues were obtained from five patients with LINCL, two with variant type NCL, three with other lysosomal storage diseases, and eight control subjects. Two antibodies were raised against N- and C-terminal peptide fragments of the normal product of the CLN2 gene. The authors examined the possibility of diagnosis of LINCL with immunostaining and immunoblotting using specific antibodies made of the recently identified defective gene in LINCL. RESULTS: Immunoreactivity with these antibodies showed the absence or marked reduction of CLN2 immunoreactivity in the lymphocytes, lymphoblasts, and fibroblasts of all five patients with LINCL examined. CONCLUSIONS: These results indicate the usefulness of this diagnostic method based on the changes in CLN2 immunoreactivity. This relatively simple, specific, and cost-effective method is a promising diagnostic tool for this disease, although additional studies are necessary.

Tertiapin potently and selectively blocks muscarinic K(+) channels in rabbit cardiac myocytes.

Tertiapin is a 21-residue peptide isolated from honey bee venoms. A recent study indicated that tertiapin is a potent blocker of certain types of inwardly rectifying K(+) (Kir) channels (). We examined the effect of tertiapin on ion channel currents in rabbit cardiac myocytes using the patch-clamp technique. In the whole-cell configuration, tertiapin fully inhibited acetylcholine (1 microM)-induced muscarinic K(+) (K(ACh)) channel currents in atrial myocytes with the half-maximum inhibitory concentration of approximately 8 nM through approximately 1:1 stoichiometry. The potency of tertiapin in inhibiting K(ACh) channels was not significantly different at -40 and -100 mV. Tertiapin also inhibited the K(ACh) channel preactivated by intracellular guanosine 5'-O-(3-thiotriphosphate), a nonhydrolyzable GTP analog. A constitutively active Kir channel, the I(K1) channel, was at least 100 times less sensitive to tertiapin. Another Kir channel in cardiac myocytes, the ATP-sensitive K(+) channel, was virtually insensitive to tertiapin (1 microM). The voltage-dependent K(+) and the L-type Ca(2+) channels were not affected by tertiapin (1 microM). At the single-channel level, tertiapin inhibited the K(ACh) channel from the outside of the membrane by reducing the NP(o) (N is the number of functional channels, and the P(o) is the open probability of each channel) without affecting the single-channel conductance or fast kinetics. Therefore, tertiapin potently and selectively blocks the K(ACh) channel in cardiac myocytes in a receptor- and voltage-independent manner. Tertiapin is a novel pharmacological tool to identify the functional role of the K(ACh) channel in the parasympathetic regulation of the heart beat.