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Biomedical subjects

S K Fong

Publications and source records attributed to S K Fong.

10 recordsLinked to original sources
PubMed1998

Neuropathy in non-insulin-dependent diabetes mellitus. The significance of symptoms.

OBJECTIVE: Clinical evaluation of significance of symptoms suggestive of neuropathy in non-insulin-dependent diabetics in general practice. DESIGN: Case control study. Interviewer-administered questionnaire. Physical examination by general practitioner researcher. SETTING: Government family practice clinic in Singapore. SUBJECTS: 55 patients with non-insulin-dependent diabetes (NIDDM) aged 35-84 years (51% males), and 53 non-diabetic controls matched for age (+/- 5 years) and gender. MAIN OUTCOME MEASURES: Proportions of subjects with presence of symptoms and physical signs. RESULTS: More patients than controls experienced symptoms suggestive of distal neuropathy (paraesthesiae: 13 vs. 4%), and lower extremity proximal myopathy (weakness climbing stairs: 42 vs. 19%, getting up from squatting position: 31 vs. 11%). No difference in proportions of patients and controls experiencing symptoms suggestive of autonomic neuropathy. More patients than controls had absent tendon reflexes (35 vs. 13%) and weaker hip muscles (24 vs. 6%). Of all who experienced symptoms indicating peripheral neuropathy, 36% of patients had absent tendon reflexes, compared with 8% of controls; and of those who experienced weakness of hip muscles, 31% of patients and 12% of controls had diminished power in the hip muscles. CONCLUSION: Symptoms suggestive of diabetic neuropathy are common and should be asked about in the routine follow-up of patients with diabetes. Up to a third of patients with symptoms will have clinical signs of diabetic neuropathy.

Adult↗
PubMed1998

Regulation of anion secretion by prostaglandin E2 in the mouse endometrial epithelium.

The present study was an investigation of the regulation of anion secretion across cultured mouse endometrial epithelium by prostaglandin E2 (PGE2) using the short-circuit current (ISC) technique. The cultured endometrial monolayers responded to both apical and basolateral application of PGE2 with a sustained rise in ISC in a concentration-dependent manner. However, the potencies of apical and basolateral addition of PGE2 were different, with apparent EC50 of 200 and 4 nM, respectively. Replacement of Cl- or HCO3- in the bathing solution significantly reduced the ISC responses to both apical and basolateral addition of PGE2; however, the apical response exhibited greater dependence on HCO3- . Pretreatment with diphenylamine 2,2'-dicarboxylic acid, a Cl- channel blocker, significantly reduced both PGE2-induced ISC responses, while pretreatment with amiloride, a Na+ channel blocker, did not exert any effect. Forskolin, an adenylate cyclase activator, and 3-isobutyl-dihydro-testosterone-1-methyl-xanthine, a cAMP phosphodiesterase inhibitor, mimicked the ISC response to PGE2 while MDL12330A, an adenylate cyclase inhibitor, completely abolished the PGE2-induced ISC. The results of the present study indicate that the anion secretion across the mouse endometrial epithelium may be regulated by PGE2 involving a cAMP-dependent mechanism predominantly. The differential responses to apical and basolateral challenge with PGE2 also suggest that PGE2 of different origins may play different roles in uterine function.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

Cellular mechanisms of adrenaline-stimulated anion secretion by the mouse endometrial epithelium.

The uterine fluid composition is largely determined by the absorptive and secretory activities of the endometrial epithelium. The present study explored the cellular mechanisms involved in adrenaline-stimulated anion secretion across the cultured mouse endometrial epithelium using the short-circuit current (ISC) technique in conjunction with transporter inhibitors and channel blockers. Cultured endometrial epithelial monolayers responded to basolateral application of adrenaline with an increase in ISC, which was attributable to both Cl- and HCO3- secretion. When extracellular Cl- or HCO3- was removed, the adrenaline-induced response, as measured by the total charge transfer per unit area, was reduced to 53% and 46%, respectively. When both Cl- and HCO3- were absent from the bathing solutions, the adrenaline-induced response was reduced to only 2% of the response when both ions were present, indicating substantial contribution of Cl- and HCO3- secretion to the adrenaline-stimulated response. Cellular mechanisms, e.g., transporters and ion channels, involved in Cl- or HCO3- secretion were investigated separately. Cl- secretion was found to depend on the activities of basolaterally located Na+-K+-ATPase, Na+-K+-2Cl- cotransporter, and K+ channels, while evidence suggested that HCO3- secretion depends substantially on basolaterally situated Na+-HCO3- cotransporter and Na+-H+ exchanger. Similar to what was seen for Cl- exit, a large portion of HCO3- appeared to exit apically through anion channels. The results indicate that the uterine fluid composition in the mouse may be regulated by adrenaline through stimulation of both Cl- and HCO3- secretion and may be fine-tuned through an elaborate operation of different cellular mechanisms.

Animals↗
PubMed1997

Stimulation of anion secretion by beta-adrenoceptors in the mouse endometrial epithelium.

1. Regulation of anion secretion by adrenoceptors in primary culture of mouse endometrial epithelium was investigated using the short circuit current (ISC) technique. 2. Adrenaline stimulated a sustained increase in the ISC in a concentration-dependent manner. The adrenaline-induced ISC could be inhibited by pretreatment with diphenylamine 2,2'-dicarboxylic acid (DPC) or replacement of external Cl- and HCO3-, but not by amiloride or replacement of Na+ in apical solution. 3. The concentration-dependent responses of the adrenaline-induced ISC to the Cl- channel blockers glibenclamide and DPC were examined and exhibited IC50 values of 380 and 960 microM, respectively. 4. The effect of various adrenoceptor agonists on the ISC was examined. The order of potency appeared to be isoprenaline > adrenaline > noradrenaline, while no response was elicited by the alpha-adrenoceptor agonist methoxamine, indicating a predominant involvement of beta-adrenoceptors. 5. The beta-adrenoceptor antagonist propranolol was found to be much more effective than the alpha-adrenoceptor antagonist phentolamine in inhibiting the ISC responses induced by all adrenoceptor agonists examined. 6. The effect of adrenaline on the ISC was mimicked by an adenylate cyclase activator, forskolin, but suppressed by the adenylate cyclase inhibitor MDL 12,330A, indicating the involvement of cAMP. 7. Our results demonstrate that anion secretion by the mouse endometrial epithelium is regulated by beta-adrenoceptors and involves a cAMP-dependent mechanism.

Adenylyl Cyclase Inhibitors↗
PubMed1997

Electrogenic ion transport in the mouse endometrium: functional aspects of the cultured epithelium.

A primary culture of mouse endometrial epithelium grown on permeable supports was established and the electrogenic ion transport across the endometrial epithelium was studied using the short-circuit current (I(SC)) technique. Enzymatically isolated mouse endometrial cells were immunostained with epithelial cells markers, cytokeratins, indicating an epithelial origin of the culture. Mouse endometrial epithelial cells grown on Millipore filters formed polarized monolayers with junctional complexes as revealed by light and electron microscopy. The cultured monolayers exhibited an average basal I(SC) of 4.6 +/- 0.3 microA/cm2, transepithelial voltage of 2.7 +/- 0.2 mV and transepithelial resistance of 599 +/- 30 omega cm2. The basal current was reduced by 85% in Na+-free solution and 13% in Cl(-)-free solution. The basal current could also be substantially (57.7%) blocked by an apical Na+ channel blocker, amiloride (10 microM), suggesting that Na+ absorption largely contributed to the basal current. Apical addition of Cl- channel blocker, DPC (2 mM), also exhibited an inhibitory effect, 19.4%, on the basal I(SC), indicating minor involvement of Cl- secretion as compared to that of Na+ absorption. The cultured endometrial epithelium also responded to a number of secretagogues including adrenaline and forskolin with increases in the I(SC), which could involve substantial Cl- secretion. The present study has established a culture of mouse endometrial epithelium exhibiting predominantly Na+ absorption under unstimulated condition, and Cl- secretion in response to various secretagogues. This culture may be useful for studying various regulatory mechanisms of electrogenic ion transport across the endometrial epithelium.

Acetylcholine↗
PubMed1997

Regulation of Cl- secretion by extracellular ATP in cultured mouse endometrial epithelium.

The present study explored regulation of electrogenic ion transport across cultured mouse endometrial epithelium by extracellular ATP using the short-circuit current (ISC) and the patch-clamp techniques. The cultured endometrial monolayers responded to apical application of ATP with an increase in ISC in a concentration-dependent manner (EC50 at 3 microM). Replacement of Cl- in the bathing solution or treatment of the cells with Cl- channel blockers, DIDS and DPC, markedly reduced the ISC, indicating that a substantial portion of the ATP-activated ISC was Cl(-)-dependent. Amiloride at a concentration (10 microM) known to block Na+ channels was found to have no effect on the ATP-activated ISC excluding the involvement of Na+ absorption. Adenosine was found to have little effect on the ISC excluding the involvement of P1 receptors. The effect of UTP, a potent P2U receptor agonist on the ISC was similar to that of ATP while potent P2X agonist, alpha-beta-Methylene adenosine 5'-triphosphate (alpha-beta-M-ATP) and P2Y agonist, 2-methylthio-adenosine triphosphate (2-M-ATP), were found to be ineffective. The effect of ATP on ISC was mimicked by the Ca2+ ionophore, ionomycin, indicating a role of intracellular Ca2+ in mediating the ATP response. Confocal microscopic study also demonstrated a rise in intracellular Ca2+ upon stimulation by extracellular ATP. In voltage-clamped endometrial epithelial cells, ATP elicited a whole-cell Cl- current which exhibited outward rectification and delayed activation and inactivation at depolarizing and hyperpolarizing voltages, respectively. The results of the present study demonstrate the presence of a regulatory mechanism involving extracellular ATP and P2U purinoceptors for endometrial Cl- secretion.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1997

Absorption kinetics of misoprostol with oral or vaginal administration.

OBJECTIVE: To compare the pharmacokinetics of vaginal and oral administration of the prostaglandin E1 analogue, misoprostol. METHODS: Twenty women received 400-micrograms doses of misoprostol either orally or as tablets placed in the vagina. Serum levels of principal metabolite, misoprostol acid, were measured at 7.5, 15, 30, 45, 60, 90, 120, and 240 minutes. The first ten women were pregnant and undergoing first-trimester abortions, and the last ten were not pregnant and had additional blood sampling at 360 minutes. We compared the pharmacokinetics of misoprostol acid after oral and vaginal administration. RESULTS: All 20 subjects completed the study. The maximum mean (+/- standard deviation [SD]) of misoprostol acid differed significantly between the oral and vaginal groups (277 +/- 124 compared with 165 +/d- 86 pg/mL, respectively; P = .03, analysis of variance), as did the mean +/- SD time to peak levels (34 +/- 17 compared with 80 +/- 27 minutes, respectively; P < .001) and areas under the misoprostol concentration versus time curve (mean +/- SD) up to 4 hours (n = 20,273.3 +/- 110.0 compared with 503.3 +/- 296.7 pg.hour/mL, respectively; P = .033) and up to 6 hours (n = 10, 300.0 +/- 103.3 compared with 956.7 +/- 541.7 pg.hour/mL, respectively; P = .029). The extent of absorption was highly variable among subjects in each group. CONCLUSION: There are significant differences in the pharmacokinetics of misoprostol administered by vaginal and oral routes that may explain the difference observed in clinical efficacy. Assuming that the pharmacologic effect of misoprostol is related to its concentration in the plasma, our observation of the prolonged serum concentrations in the vaginal group suggests that vaginal administration could be dosed at longer intervals than oral.

Abortifacient Agents, Nonsteroidal↗
PubMed1991

Wild-type and mutant bacterioopsins D85N, D96N, and R82Q: high-level expression in Escherichia coli.

The integral membrane protein bacterioopsin, found in the extremely halophilic archaebacterium Halobacterium halobium, was expressed in Escherichia coli as a fusion protein containing 13 heterologous amino acids at the amino terminus. The expressed protein was localized primarily to the E. coli cytoplasmic membrane (greater than 80%) and had an in vivo half-life of 26 min. The amount of bacterioopsin in E. coli crude lysates was quantitated immunologically from Western blots and was expressed at 10-20-fold higher levels than seen previously (i.e., 17 mg/L; 5.6% of the total protein). Three distinct forms of the protein were detected immunologically: two of the forms were generated by the removal of either one or four amino acid residues at the amino terminus; the third form remained unaltered.

Amino Acid Sequence↗
PubMed1991

Wild-type and mutant bacteriorhodopsins D85N, D96N, and R82Q: purification to homogeneity, pH dependence of pumping, and electron diffraction.

Bacterioopsin, expressed in Escherichia coli as a fusion protein with 13 heterologous residues at the amino terminus, has been purified in the presence of detergents and retinylated to give bacteriorhodopsin. Further purification yielded pure bacteriorhodopsin, which had an absorbance ratio (A280/A lambda max) of 1.5 in the dark-adapted state in a single-detergent environment. This protein has a folding rate, absorbance spectrum, and light-induced proton pumping activity identical with those of bacteriorhodopsin purified from Halobacterium halobium. Protein expressed from the mutants D85N, D96N, and R82Q and purified similarly yielded pure protein with absorbance ratios of 1.5. Proton pumping rates of bacteriorhodopsins with the wild-type sequence and variants D85N, D96N, and R82Q were determined in phospholipid vesicles as a function of pH. D85N was inactive at all pH values, whereas D96N was inactive from pH 7.0 to pH 8.0, where wild type is most active, but had some activity at low pH. R82Q showed diminished proton pumping with the same pH dependence as for wild type. Bacteriorhodopsin purified from E. coli crystallized in two types of two-dimensional crystal lattices suitable for low-dose electron diffraction, which permit detailed analysis of structural differences in site-directed variants. One lattice was trigonal, as in purple membrane, and showed a high-resolution electron diffraction pattern from glucose-sustained patches. The other lattice was previously uncharacterized with unit cell dimensions a = 127 A, b = 67 A, and symmetry of the orthorhombic plane group pgg.

Bacteriorhodopsins↗