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C A Wang

Publications and source records attributed to C A Wang.

At least 19 recordsLinked to original sources

Rapid nongenomic effect of corticosterone on neuronal nicotinic acetylcholine receptor in PC12 cells.

The effects of corticosterone, a natural glucocorticoid of rat, on the acetylcholine (ACh)-induced current (I(ACh)) were studied in pheochromocytoma (PC12) cells by using whole-cell clamp technique. The I(ACh) proved to be generated through neuronal nicotinic receptor. ACh (30 microM) induced an inward current at a holding potential of -80 mV. When cells were preincubated with corticosterone (0.1-100 microM) for 4 min, an inhibitory effect of corticosterone on the peak of I(ACh) was found. This effect was reversible, concentration-dependent, and voltage-independent. Intracellular application of corticosterone through the patch electrode did not affect the I(ACh). Extracellular application of 10 microM corticosterone neither shifted the dose-response curve of the peak I(ACh) to the right (dissociation constant (K(d)) = 16.5 microM) nor affected its coefficient (1.8) but inhibited the curve amplitudes by approximately 49% in the cells pretreated with corticosterone for 4 min. Bovine serum albumin-conjugated corticosterone (0.1-10 microM) had the inhibition similar to corticosterone. The inhibitor of transcription, actinomycin D (10 microM), and the protein synthesis inhibitor, cycloheximide (50 microM), had no effect on the inhibition induced by corticosterone on I(ACh). These results suggest that corticosterone has rapid inhibitory effect on I(ACh) in PC12 cells, which is mediated by a nongenomic mechanism. It indicates that corticosterone binds to the specific site on the outer cell membrane, probably on the neuronal nicotinic receptor-coupled channel, and inhibits the I(ACh) in a noncompetitive manner, thus controlling the immediate catecholamine release from the sympathetic cells.

Acetylcholine↗

Restoration of decreased N-methyl-d-asparate receptor activity by brain-derived neurotrophic factor in the cultured hippocampal neurons: involvement of cAMP.

Brain-derived neurotrophic factor (BDNF) may play an important role in the modulation of N-methyl-d-asparate (NMDA) receptor function. To elucidate the underlying mechanisms, whole-cell patch-clamp recording was used to assess the effect of BDNF on the responses of cultured hippocampal neurons to the glutamate receptor agonist NMDA. We found that peak amplitude of NMDA-evoked currents in cultured hippocampal pyramidal neurons at Day 18 in vitro decreased significantly compared to that of NMDA currents at Day 10 or 14. Interestingly, NMDA-evoked currents were greatly enhanced by BDNF (50 ng/ml) in cultured neurons at Day 18, but not at Day 10 or 14. Treatment with Rp-cAMP abolished the potentiating effects of BDNF on NMDA current. Elevating the amount of cytosolic cAMP by preincubation with forskolin or Sp-cAMP also enhanced NMDA currents as effectively as BDNF in 18-day-old hippocampal neurons. Measurement of the cellular content of cAMP by RIA indicated that cultured hippocampal neurons showed decreased basal cAMP levels at the time NMDA currents were decreased and BDNF increased the decreased cAMP levels. Taken together, these results suggest that BDNF may restore decreased NMDA receptor activity in cultured hippocampal neurons by the cAMP pathway.

Animals↗

Calmodulin levels are dynamically regulated in living vascular smooth muscle cells.

The total unbound calmodulin (i.e., not bound to target proteins) level in living smooth muscle cells from the ferret portal vein was monitored with a low-affinity, calmodulin-binding peptide tagged with an environmentally sensitive fluorophore. GS17C, a previously characterized peptide, from the calmodulin-binding domain of caldesmon was tagged with iodoacetyl nitrobenz-2-oxa-1,3-diazole (NBD) or, as a negative control, with iodoacetylfluorescein isothiocyanate. Increases in NBD-GS17C fluorescence were detected by using confocal microscopy when chemically loaded cells were stimulated with solutions of elevated [K(+)] or the calcium ionophore 4-bromoA-23187 to elicit increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) quantified by fura 2. Increases in peptide fluorescence were detected in response to a phorbol ester in the absence of changes in [Ca(2+)](i). These changes were blocked by the addition of the calmodulin antagonist calmidazolium. These results suggest that the total unbound intracellular calmodulin levels may be sufficient to regulate the activity of caldesmon and, furthermore, that phosphorylation of protein kinase C substrates may increase the level of available calmodulin in living smooth muscle cells.

4-Chloro-7-nitrobenzofurazan↗

The major myosin-binding site of caldesmon resides near its N-terminal extreme.

The primary myosin-binding site of caldesmon was thought to be in the N-terminal region of the molecule, but the exact nature of the caldesmon-myosin interaction has not been well characterized. A caldesmon fragment that encompasses residues 1-240 (N240) was found to bind full-length smooth muscle myosin on the basis of co-sedimentation experiments. The interaction between myosin and N240 was not affected by phosphorylation of myosin, but it was weakened by the presence of Ca(2+)/calmodulin. To locate the myosin-binding site, we have designed several synthetic peptides based on the N-terminal caldesmon sequence. We found that a peptide stretch corresponding to the first 27 residues (Met-1 to Tyr-27), but not that of the first 22 residues (Met-1 to Ala-22), exhibited a moderate affinity toward myosin. We also found that a peptide containing the segment from Ile/Leu-25 to Lys-53 bound both myosin and heavy meromyosin more strongly and was capable of displacing caldesmon from myosin. Our results demonstrate that the sequence near the N-terminal extreme of caldesmon harbors a major myosin-binding site of caldesmon, in which both the nonpolar residues and clusters of positively and negatively charged residues confer the specificity and affinity of the caldesmon-myosin interaction.

Amino Acid Sequence↗

Calmodulin remains extended upon binding to smooth muscle caldesmon: a combined small-angle scattering and fourier transform infrared spectroscopy study.

We show that calmodulin (CaM) has an extended conformation in its complexes with sequences from the smooth muscle thin filament protein caldesmon (CaD) by using small-angle X-ray and neutron scattering with contrast variation. The CaD sequences used in these experiments were a C-terminal fragment, 22kCaD, and a smaller peptide sequence within this fragment, MG56C. Each of these sequences contains the CaM-binding sites A and B previously shown to interact with the C- and N-terminal lobes of CaM, respectively [Wang et al. (1997) Biochemistry 36, 15026]. By modeling the scattering data, we show that the majority of the MG56C sequence binds to the N-terminal domain of CaM. FTIR data on CaM complexed with 22kCaD or with MG56C peptide show the 22kCaD sequence contains unordered, helix, and extended structures, and that the extended structures reside primarily in the MG56C portion of the sequence. There are small changes in secondary structure, involving approximately 12 residues, induced by CaM binding to CaD. These changes involve a net decrease in extended structures accompanied by an increase in alpha-helix, and they occur within the CaM and/or in the MG56C sequence.

Animals↗

Regulation of vascular smooth muscle tone by N-terminal region of caldesmon. Possible role of tethering actin to myosin.

To assess the functional significance of tethering actin to myosin by caldesmon in the regulation of smooth muscle contraction, we investigated the effects of synthetic peptides, containing the myosin-binding sequences in the N-terminal region of caldesmon, on force directly recorded from single permeabilized smooth muscle cells of ferret portal vein. Two peptides were used, IK29C and MY27C, containing residues from Ile(25) to Lys(53) and from Met(1) to Tyr(27) of the human and chicken caldesmon sequence, respectively, plus an added cysteine at the C terminus. In cells clamped at pCa 6. 7, both peptides increased basal tone. Pretreatment of cells at pCa 6.7 with IK29C or MY27C decreased the amplitude of subsequent phenylephrine-induced contractions but not microcystin-racemic mixture-induced contractions. In all cases the effects of the peptides were concentration-dependent, and IK29C was more potent than MY27C, in agreement with their relative affinity toward myosin. The peptides were ineffective after the phenylephrine contraction was established. MY27C did not further increase the magnitude of contraction caused by a maximally effective concentration of IK29C, consistent with the two peptides having the same mechanism of action. Neither polylysine nor two control peptides containing scrambled sequences of IK29C, which do not bind myosin, had any effect on basal or phenylephrine-induced force. Our results suggest that IK29C and MY27C induce contraction by competing with the myosin-binding domain of endogenous caldesmon. Digital imaging of fluoroisothiocyanate-tagged IK29C confirmed the association of the peptide with intracellular filamentous structures. The results are consistent with a model whereby tethering of actin to myosin by caldesmon may play a role in regulating vascular tone by positioning the C-terminal domain of caldesmon so that it is capable of blocking the actomyosin interaction.

Amino Acid Sequence↗

Effect of forskolin on acetylcholine-induced current in rat pheochromocytoma cells.

AIM: To study the effect of forskolin on the nicotinic receptor (NicR) of PC12 cells. METHODS: The acetylcholine (ACh)-induced current (IACh) was measured on PC12 cells by whole-cell clamp technique. RESULTS: The IACh could be blocked by d-tubocurarine chloride and atropine had no effect on IACh. Infusion of forskolin (1-50 mumol.L-1) caused an inhibition on IACh, which was reversible, concentration-dependent, and voltage-independent. Preincubation with 8-bromo-adenosine-3', 5'-adenosine monophosphate (8-Br-cAMP), a cell-permeable cAMP analog which preferentially activated cyclic AMP-dependent protein kinase (CADPK), for 20 min, did not affect the IACh and the inhibitory effect of forskolin. Infusion of 1,9-dideoxyforskolin, an analog of forskolin which did not activate adenyl cyclase, also caused an inhibition on IACh. CONCLUSION: The inhibitory effect of forskolin on IACh in PC12 cells is not mediated by activating the adenyl cyclase. Probably, the lipophilic forskolin acts via perturbing the plasma membrane lipid structure and altering the function of the NicR.

8-Bromo Cyclic Adenosine Monophosphate↗

Mammal-specific, ERK-dependent, caldesmon phosphorylation in smooth muscle. Quantitation using novel anti-phosphopeptide antibodies.

Extracellular signal-regulated kinases (ERKs) phosphorylate the high molecular mass isoform of the actin-binding protein caldesmon (h-CaD) at two sites (Ser(759) and Ser(789)) during smooth muscle stimulation. To investigate the role of phosphorylation at these sites, antibodies were generated against phosphopeptides analogous to the sequences around Ser(759) and Ser(789). Affinity-purified antibodies were phosho- and sequence-specific. The major site of phosphorylation in h-CaD in porcine carotid arterial muscle strips was at Ser(789); however, the amount of phosphate did not vary appreciably with either KCl or phorbol ester stimulation. Phosphorylation at Ser(759) of h-CaD was almost undetectable (<0.005 mol of phosphate/mol of protein). Moreover, phosphorylation of the low molecular mass isoform of the protein (l-CaD) at the site analogous to Ser(789) was greater in serum-stimulated cultured smooth muscle cells than in serum-starved cells. Serum-stimulated l-CaD phosphorylation was attenuated by the protein kinase inhibitor PD98059. These data 1) identify Ser(789) of h-CaD as the major site of ERK-dependent phosphorylation in carotid arteries; 2) show that the level of phosphorylation at Ser(789) is relatively constant following carotid arterial muscle stimulation, despite an increase in total protein phosphate content; and 3) suggest a functional role for ERK-dependent l-CaD phosphorylation in cell division.

Amino Acid Sequence↗

[Rapid inhibitory effect of glucocorticoids on ACh-induced current in rat phaeochromocytoma cells].

A rapid effect of glucocorticoids (GC) on acetycholine-induced current in rat phaeochromocytoma (PC12) cells and its possible mechanism were investigated by whole-cell clamp technique. The results are as follows: The acetylcholine-induced current (IACh) of PC12 cells was proved to be generated through nicotinic ACh receptor by pharmacological identification. ACh (30 mumol/L) induced an inward current at a holding potential (Vh) of -80 mV. The inhibitory effect of corticosterone (B) on IACh was weak when 10(-5) mol/L B and ACh were simultaneously applied extracellularly. Pretreatment of PC12 cells with B could augment the inhibitory effect on peak IACh, and this dose-dependent effect was reversible. At the same concentration of GC, the rank of the inhibitory potency was B > dexamethasone (Dex) > hydrocortisone (F). Extracellular application of B-BSA could also inhibit IACh rapidly. Taken together, it is suggested that GC induced rapid inhibitory effects on IACh in PC12 cells are probably mediated by a nongenomic mechanism. The inhibitory effect of various GC on IACh are different.

Acetylcholine↗

Calponin and mitogen-activated protein kinase signaling in differentiated vascular smooth muscle.

Contraction of smooth muscle cells is generally assumed to require Ca2+/calmodulin-dependent phosphorylation of the 20-kDa myosin light chains. However, we report here that in the absence of extracellular calcium, phenylephrine induces a contraction of freshly isolated ferret aorta cells in the absence of increases in intracellular ionized calcium or light chain phosphorylation levels but in the presence of activation of mitogen-activated protein kinase. A protein at 36 kDa co-immunoprecipitated with the mitogen-activated protein kinase and was identified as the actin-binding protein, calponin, by immunoblot. An overlay assay further confirmed an interaction between the kinase and calponin, even though the kinase did not phosphorylate calponin in vitro. Calponin also co-immunoprecipitated from smooth muscle cells with protein kinase C-epsilon. High resolution digital confocal studies indicated that calponin redistributes to the cell membrane during phenylephrine stimulation at a time when mitogen-activated protein kinase and protein kinase C-epsilon are targeted to the plasmalemma. These results suggest a role for calponin as a signaling molecule, possibly an adapter protein, linking the targeting of mitogen-activated protein kinase and protein kinase C-epsilon to the surface membrane.

Animals↗

Heat treatment could affect the biochemical properties of caldesmon.

Smooth muscle caldesmon (CaD) exhibits apparent heat stability. A widely used purification procedure of CaD involves extensive heat treatment (Bretscher, A. (1984) J. Biol. Chem. 259, 12873-12880). CaD thus purified co-sediments with actin, inhibits actomyosin ATPase activity, and interacts with Ca2+/calmodulin, similarly to the unheated protein. On the other hand, heat-treated CaD binds to actin filaments in a tether-like fashion, whereas lengthwise binding dominates in vivo (Mabuchi, K., Lin, J. J.-C., and Wang, C.-L. A. (1993) J. Muscle Res. Cell Motil. 14, 54-64), suggesting that differences do exist between heat-purified CaD and the native protein. We have isolated, without heat treatment, full-length recombinant chicken gizzard CaD overexpressed in insect cells (High-FiveTM) using a baculovirus expression system. We found that such unheated CaD interacts with calmodulin 10 times stronger than does the heated CaD; its inhibitory action on actomyosin ATPase is reversed by a much lesser amount of calmodulin. Moreover, electron microscopic examination indicated that actin binding at the N-terminal region is more frequent in the unheated CaD, resulting in more lengthwise binding. These findings point to the fact that CaD is not entirely heat-stable; the C-terminal CaM-binding regions and the N-terminal actin-binding region are possibly affected by heat treatment.

Actins↗

[Bovine serum albumin-conjugated corticosterone inhibits the release of arginine vasopressin].

The arginine vasopressin (AVP) released from rat hypothalamic slices containing paraventricular and supraoptic nuclei sectioned with vibratome and incubated in microchambers was measured by radioimmunoassay. The effect of bovine serum albumin-conjugated corticosterone (B-BSA) on the AVP release was investigated. The results were as follows: (1) B-BSA, within 20 min, inhibited the AVP release in a dose-dependent manner from 10(-7) to 10(-4) mol/L. (2) The inhibitory effect of B-BSA was partially blocked by RU486 (10(-4)-10(-3) mol/L). (3) With the elevation of Ca2+ in the incubation medium the inhibitory effect of B-BSA was enhanced. (4) The inhibitory effect of B-BSA was also enhanced in the presence of neomycin (10(-3)-10(-2) mol/L). These results suggested that glucocorticoid, without entering into cells, could inhibit AVP release from rat hypothalamic slices. This effect might be mediated via a non-genomic mechanism involving a change of Ca2+ influx across the cell membrane.

Animals↗

Nongenomic effect of glucocorticoid on the release of arginine vasopressin from hypothalamic slices in rats.

The arginine vasopressin (AVP) released from the hypothalamic slices containing paraventricular and supraoptic nuclei of Sprague-Dawley rats sectioned with vibratome and incubated in static microchambers was measured by radioimmunoassay, and the rapid effect and its underlying mechanism of glucocorticoids (GC) on AVP release were investigated. The results were as follows: (1) AVP was steadily released at a rate of 9.1 +/- 1.2 pg/min/well for as long as 6 h. (2) Corticosterone (B), within 20 min, inhibited AVP release in a dose-dependent manner from 10(-7) to 10(-4) mol/l. (3) Cortisol, 17beta-estradiol, or testosterone (all in 10(-6) mol/l) to some extent also inhibited AVP release, but dexamethasone, aldosterone, progesterone, RU 38486 or cholesterol had no significant inhibition on AVP release. (4) The rapid inhibitory effect of B was not affected by actinomycin D, puromycin or colchicine. (5) RU 38486 (10(-5)-10(-3) mol/l) could partially block the rapid inhibitory effect of B, although it did not by itself change AVP release. (6) With the elevation of Ca2+ in the incubation medium, the AVP release was increased and the rapid inhibitory effect of B enhanced; while in the absence of Ca2+ the AVP release decreased and the effect of B attenuated. (7) The rapid inhibitory effect of B was enhanced in the presence of neomycin, although the latter had no influence on AVP release. (8) Aminophylline did not affect the rapid inhibitory effect of B. These results indicated that the rapid inhibitory effect of GC might be a nongenomic rather than the classical genomic one, and that the extracellular Ca2+ play a role in the rapid effect of GC on AVP release. The significance of the rapid action of GC in the rapid negative feedback regulation of AVP release from hypothalamus of rats was discussed.

Animals↗

[Effect of glucocorticoids and other steroids on arginine vasopressin release from rat hypothalamic slices].

Rat hypothalamic slices sectioned with vibratome (containing paraventricular and supraoptic nuclei) were incubated in static microchamber and the Arginine vasopressin (AVP) released from the slices was measured by radioimmunoassay. The effect of glucocorticoids (GC) and other steroids on AVP release was investigated. The results were as follows: (1) AVP was steadily released at a rate of 9.06 +/- 1.23 pg/min for as long as 6 h (not including the 90 min for recovery of slices). (2) Corticosterone (B) inhibited AVP release within 20 min in a dose-dependent manner from 10(-7) to 10(-4) mol/L. (3) Cortisol, 17 beta-estradiol, or testosterone (10(-6) mol/L) also inhibited AVP release within 20 min, but dexamethasone, aldosterone, progesterone, RU486, or cholesterol had no significant effect. (4) RU486 (10(-5)-10(-3) mol/L) could partially block the rapid inhibitory effect of corticosterone. These results suggested that GC might exert in situ a regulatory negative feedback action on the AVP release from hypothalamus of rat through a non-genomic rather than a genomic mechanism.

Animals↗

[Evaluation of radiation doses in mammography].

A dedicated X-ray mammography was introduced to our hospital from 1987 and an imaging receptor of xeroradiography was applied. We reported previously that the average air exposure was 0.79R and that the absorption dose of skin was 1.00 rad. These data are similar to literature reports. Screen-film mammography was introduced recently. To select the best breast imaging and the least radiation exposure, diverse methods were investigated. A dosimetry (Capintec model 192) and a PS-033 parallel ionization chamber were applied to compare the absorption dose on polystyrene phantom between various exposure factors, the application of breast clamp and the size of exposure field. Retrospective estimation of the radiation dose was obtained from the exposure factors of previous mammography since July, 1990 to May, 1992. There were 1035 xeromammographic examinations and 358 examinations with medium-speed screen-film mammography. Another 61 craniocaudal and 96 mediolateral projections with high-speed screen-film mammography were recruited during the recent two months. An ionization chamber (Exradin, Shonka-Wyckoff A5) with an electrometer (Keithley 617) wer selected to obtain the dose equivalent from air exposure between selected exposure factors. The radiation dose of mammography is linearly correlated with voltage/kV and current/mAs. The application of a breast clump reduces 10% of the skin dose. The average exposure factors of xeromammography are 45.6 kV, 163.5 mAs. These results remain the same as in our previous report. Xeromammography has a greater exposure to air, estimated average glandular dose and absorbed dose than screen-film mammography. The mean exposure factor of rapid screen-film mammography gains half the value of medium screen-film mammography, ie. 26.6 kV, 87.0 mAs vs. 26.0 kV, 164.5 mAs.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗

An electrophysiological study on the membrane receptor-mediated action of glucocorticoids in mammalian neurons.

The action of glucocorticoids (GC) on neuronal cell membrane was studied in isolated and superfused guinea pig coeliac ganglia by the intracellular recording technique. Cortisol succinate (F) hyperpolarized the membrane potential of 47 of 179 cells and changed the cell's input resistance with a latency of less than 2 min in vitro. The effect persisted under low Ca2+/high Mg2+ superfusing condition and could be blocked by RU 38486, a competitive antagonist of GC cytosolic receptor. Cortisol-21-bovine albumin conjugant exhibited the same effect. Corticosterone (B) elicited hyperpolarization in another 15 of 83 cells, but dexamethasone (Dex) did not. Dex, however, depolarized 2 of 18 cells. Aldosterone, cholesterol and vehicle (ethyl alcohol) caused no detectable change in membrane potential. In vivo studies by iontophoretic application of steroids to hypothalamic paraventricular (PVN) neurons showed that F inhibited the unit discharges in 68 of 97 PVN neurons, and the effect could be antagonized by RU 38486. Dex excited 30 of 100 neurons. Estradiol (E) also inhibited the discharges, but this inhibition was not antagonized by RU 38486. The effect of GC on PVN neurons was also examined in hypothalamic slices including the paraventricular nucleus. B inhibited 28 of 104 units and excited 7 of 104 cells, and both effects could be antagonized by RU 38486. The threshold of inhibitory response was about 10(-7) M, which is close to the physiological level of the hormone in plasma. The results suggest that GC can act non-genomically and specifically through its membrane receptor on the neuronal surface, and that there might be a chemical similarity between the membrane receptor and the traditional cytosolic GC receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

[The rapid effect of the iontophoretically applied cortisol on unit activity of neurons in three brain areas in rats].

The present study was undertaken to analyze whether the glucocorticoid (GC) effect was region specific in the brain. Na-cortisol-succinate (HC) was applied iontophoretically to cerebral cortex (CX), hippocampus (HPC) and PVN respectively and the effect on unit discharge rate in these three brain areas were compared. In cerebral cortex, the percentage of responsive neurons was only 8% (4/50), which was significantly lower than those in HPC (10/36, 27.8%) and PVN (9/35, 25.7%). The difference in the occurrence is paralleled with the known distribution of traditional GC cytosolic receptors in the brain. In all the three brain areas studied the main response to GC was inhibitory and the latencies of the responses were 9.6 +/- 6.5, 22.7 +/- 24.0, and 14.5 +/- 11.5 s and the durations of the after-effect were 74.8 +/- 66.5 (n = 4), 24.2 +/- 14.5 (n = 6) and 21.0 +/- 10.5 s (n = 9) respectively. The shortness of the latencies once again suggests that the mechanism involved is non-genomic. It is interest to note that in some HPC neurons the after-effect lasted for 1758 +/- 2148 s (n = 4). The results show that the rapid effect of GC on neurons is different in the three brain areas studied in regarding to the occurrence of responsive neurons and the duration of the after-effects.

Animals↗

[Responses of midbrain central gray neurons activated by hypothalamic paraventricular nucleus (PVH) stimulation to somatic afferent input in rats].

Extracellular single unit recordings were made from 318 neurons within the midbrain central gray in urethane-anesthetized rats. Following electrical stimulation of the hypothalamic paraventricular nucleus (PVH), 10% of the units in central gray (CG) were antidromically activated, while 7.5% were orthodromically excited, and 0.7% were orthodromically inhibited. Among these antidromically activated neurons, 28 units were further examined for their responsiveness to peripheral somatic sensory stimulation. Strong electrical stimulation of contralateral sciatic and tibial nerve, and tail pinching produced excitation in 12 and inhibition in 2 units. No significant responses to non-noxious stimulation were observed in these units. Of the 26 orthodromically activated units, 14 were excited and 4 inhibited by the sciatic nerve stimulation or tail pinching. These results support the hypothesis that CG is one of the relay stations in the afferent pathway of somatic sensory especially, noxious, information transmitting to the PVH, and that the PVH may play a role in central pain control or modulation via their descending influence on CG unit.

Animals↗