[Drug therapy in the treatment of glaucoma].
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Adrenergic beta-Antagonists↗
Biomedical subjects
H Thieme
Publications and source records attributed to H Thieme.
Muscarinic receptors of the M2 subtype in human and bovine trabecular meshwork.
BACKGROUND: The trabecular meshwork is a tissue actively involved in the regulation of intraocular pressure via contractile mechanisms. The present study was performed to investigate the effects of muscarinic m2-receptor antagonists on trabecular meshwork contractility and to identify the m2 muscarinic receptor in human and bovine trabecular meshwork cells. METHODS: Isometric tension measurements of bovine trabecular meshwork strips were performed using a custom-made force length transducer. Western blot and immunoprecipitation analysis was used to detect the m2-receptor proteins in membrane preparations of human and bovine trabecular meshwork cells. RESULTS: Immunoblotting results showed the expression of an m2-receptor protein band at 56 kDa in both human and bovine trabecular meshwork cells. Two different m2-receptor antagonists were tested on trabecular meshwork contractility. After carbachol-induced contraction (10(-6) M set to 100% contractile force), specific m2-receptor antagonists were applied. 3 alpha-Chloroimperaline (10(-6) M) had no effect on the maximal carbachol-induced contraction in trabecular meshwork strips. Methoctramine induced a significant relaxation at concentrations of 10(-7), 10(-6) and 5 x 10(-6) M even in the presence of m1- and m3-receptor antagonists. CONCLUSION: These data indicate that in addition to the m3-receptor subtype present in the trabecular meshwork this tissue also features the m2 receptor. This receptor is partly involved in the regulation of trabecular meshwork contractility, suggesting that outflow facility might be influenced through this receptor.
Animals↗
Flufenamic acid enhances current through maxi-K channels in the trabecular meshwork of the eye.
PURPOSE: Flufenamic acid relaxes trabecular meshwork, a smooth muscle-like tissue involved in the regulation of ocular outflow in the eye. In this study, we attempted to determine if ionic channels are involved in this response. METHODS: Cultured human (HTM) and bovine (BTM) trabecular meshwork cells were investigated using the patch-clamp technique. RESULTS: In trabecular meshwork, flufenamic acid (10(-5) M) reversibly stimulated outward current to 406 +/- 71% of initial outward current level in BTM (n = 10) and 294 +/- 75% of initial current level in HTM (n = 12) in all cells investigated; no significant differences emerged. The response was dosage-dependent. Replacement of potassium in all solutions eliminated the response to flufenamic acid (n = 4, BTM). Blocking K(ATP ) channels with glibenclamide (10(-5) M, n = 6) and small-conductance calcium-activated potassium channels with apamin (10(-6) M, n = 5) had no effect. A direct effect on calcium channels could also not be detected. Blockage of the large-conductance calcium-activated potassium channel (maxi-K) by iberiotoxin (10(-7) M) suppressed 87 +/- 9% (n = 6; HTM) and 91 +/- 10% (n = 6; BTM) of the response. Depleting the cells of calcium did not significantly alter the response to flufenamic acid. CONCLUSIONS: Flufenamic acid stimulates maxi-K channels in trabecular meshwork of both human and bovine origin. This should lead to hyperpolarization, closure of L-type channels and lowered cytosolic calcium levels, possibly explaining the relaxation observed in response to this substance.
Animals↗
Fibroblast growth factor receptor 2 (FGFR2) in brain neurons and retinal pigment epithelial cells act via stimulation of neuroendocrine L-type channels (Ca(v)1.3).
In contrast to the fibroblast growth factor receptor 1 (FGFR1), little is known about intracellular signaling of FGFR2. The signaling cascade of FGFR2 was studied using the perforated patch configuration of the patch-clamp technique in cultured rat retinal pigment epithelial (RPE) cells that express both FGFR1 and FGFR2. Interaction of signaling proteins was studied using immunoprecipitation techniques with membrane proteins from RPE cells and freshly isolated rat brain. When Ba(2+) currents through L-type channels were studied, extracellular application of bFGF (10 ng/ml) led to a shift of the steady-state activation to more negative values. In 50% of cells, an additional increase in maximal current amplitude was observed. This effect was blocked by the tyrosine kinase inhibitor lavendustin A (10(-5) M) but was not influenced by the FGFR1 blocker SU5402 (2 x 10(-5) M) or by the blocker for src-kinase herbimycin A (10(-5) M). Immunoprecipitation of FGFR2 led to coprecipitation of alpha 1D Ca(2+) channel subunits and precipitation of alpha 1D subunits led to coprecipitation of FGFR2. Immunoprecipitation of FGFR1 did not result in the coprecipitation with alpha 1D Ca(2+) channel subunits. The coprecipitation results were comparable when using brain tissue and RPE cells. The alpha 1D subunit-specific band were stained with antiphosphotyrosine antibodies. We conclude that FGFR2 acts via a different signaling cascade than FGFR1. This cascade involves an src-kinase-independent, close functional interaction of FGFR2 and the alpha subunit of neuroendocrine L-type channels.
Animals↗
Mechanisms of action of unoprostone on trabecular meshwork contractility.
PURPOSE: This study was performed to clarify the possible mechanism behind the ocular hypotensive effect of unoprostone isopropyl (Rescula; Novartis Ophthalmics AG, Basel, Switzerland), a new docosanoid that has been shown to reduce intraocular pressure (IOP) in patients with ocular hypertension or primary open-angle glaucoma. To gain insight into the possible mode of action, the effects of unoprostone on ciliary muscle (CM) and trabecular meshwork (TM) contractility, intracellular calcium levels, and membrane channels were investigated. METHODS: The effects of unoprostone (M1 metabolite = free acid, 10(-5) M) and endothelin (ET)-1 (10(-9) M) on bovine TM (BTM) and ciliary muscle (CM) strips were investigated, by using a custom-made force-length transducer system. The effects of unoprostone and ET-1 (5 x 10(-8) M) on intracellular Ca(2+) mobilization in cultured human TM (HTM) were measured using fura-2AM as a fluorescent probe. Patch-clamp experiments were performed on HTM and BTM cells to investigate the unoprostone-dependent modulation of membrane currents. RESULTS: In isolated TM and CM strips, unoprostone almost completely inhibited ET-induced contractions (TM: 2.9% +/- 4.3% vs. 19.6% +/- 5.7%, P < 0.05, n = 6; CM: 1.4% +/- 1.6% vs. 30.1% +/- 5.3%, P < 0.01, n = 6; 100% = maximal carbachol-induced (10(-6) M) contraction). However, neither carbachol-induced contraction nor baseline tension was affected by unoprostone. Furthermore, unoprostone had no effect on baseline intracellular calcium levels (baseline: 126 +/- 45 nM versus unoprostone: 132 +/- 42 nM, n = 8) in HTM cells. The endothelin-induced increase (679 +/- 102 nM), however, was almost completely (P < 0.01) blocked by unoprostone (178 +/- 40 nM). In patch-clamp recordings, unoprostone could be shown to double the amplitude of outward current (HTM: 200% +/- 33%; n = 6; BTM: 179% +/- 20%; n = 8). This effect was blocked by the specific inhibitor of maxi-K channels, iberiotoxin. CONCLUSIONS: This study presents evidence for direct interaction of unoprostone with the contractility of the TM and CM. This compound may lower IOP by affecting aqueous outflow, most probably conventional outflow pathways (i.e., TM) through inhibition of ET-dependent mechanisms. In addition, unoprostone interacts with the maxi-K channel. Although primarily Ca(2+)-sensitive signal-transduction pathways seem to be involved, effects of unoprostone on Ca(2+)-independent pathways and uveoscleral outflow cannot be excluded.
Adult↗
Activation of neuroendocrine L-type channels (alpha1D subunits) in retinal pigment epithelial cells and brain neurons by pp60(c-src).
The aim of this study is to characterize the subtype of tyrosine kinase-regulated L-type Ca(2+) channels in retinal pigment epithelial (RPE) cells. Ca(2+) channel alpha1D-subunits were enriched by immunoprecipitation from membrane proteins isolated from rat RPE cells. Western blot analysis of the precipitates revealed coprecipitation of pp60(c-src). In addition, in precipitates obtained with antibodies against pp60(c-src), alpha1D-subunits were identified. The same was observed in immunoprecipitations from rat brain neurons. Tyrosine phosphorylation of alpha1D-subunits was confirmed using anti-phosphotyrosine antibodies. Ba(2+) currents through L-type channels in cultured rat RPE cells were increased by intracellular application of active pp60(c-src) (30 U/ml) (heat-inactivated pp60(c-src) had no effect). Thus, L-type channels of the neuroendocrine subtype can be expressed in epithelial cells and are activated by tyrosine kinase of the src subtype. This kind of regulation is also suggested for brain-derived neurons.
Animals↗
Influence of muscarinic agonists and tyrosine kinase inhibitors on L-type Ca(2+)Channels in human and bovine trabecular meshwork cells.
Trabecularmeshwork (TM), a smooth muscle-like tissue with contractile properties, is involved in the regulation of aqueous humor outflow. However, little is known about the regulation of Ca(2+)influx in trabecular meshwork cells. We investigated the influence of acetylcholine and tyrosine kinases on Ca(2+)conductances of bovine TM (BTM) and human TM (HTM) cells using the perforated-patch configuration of the patch-clamp technique and measurements of intracellular free Ca(2+)([Ca(2+)](i)). Depolarization of the cells in the presence of 10 m m Ba(2+)or Ca(2+)led to an activation of inward currents at potentials positive to -30 mV with characteristics typical of L-type Ca(2+)currents: when using 10 m m Ba(2+), maximal inward current and inactivation time constant (tau) increased; the L-type Ca(2+)channel blocker nifedipine (1 microm) reduced and the L-type Ca(2+)channel agonist BayK8644 (5 microm) enhanced maximal inward current. Acetylcholine (100 microm) and carbachol (1 microm) led to an increase in inward Ba(2+)current whereas application of the tyrosine kinase inhibitors genistein (50 microm) and lavendustin A (20 microm) resulted in a decrease in inward current. The application of daidzein (10 microm), an inactive analog of genistein had no effect. Depolarization of the cells with 135 m m K(+)or direct stimulation of L-type channels by application of BayK 8644 led to an increase in [Ca(2+)](i). Carbachol (1 microm) induced an increase in [Ca(2+)](i)which was decreased by application of the tyrosine kinase inhibitor genistein (50 microm). We conclude that HTM and BTM cells express voltage-dependent L-type Ca(2+)channels that influence intracellular Ca(2+)concentration and thus may modulate TM contractility. The activity of L-type Ca(2+)currents is influenced by muscarinic agonists and tyrosine kinases.
Acetylcholine↗
The regulation of trabecular meshwork and ciliary muscle contractility.
Current models of aqueous humor outflow no longer treat trabecular meshwork (TM) as an inert tissue passively distended by the ciliary muscle (CM). Instead, ample evidence supports the theory that trabecular meshwork possess smooth muscle-like properties and is actively involved in the regulation of aqueous humor outflow and intraocular pressure. In this model, trabecular meshwork and ciliary muscle appear as functional antagonists, with ciliary muscle contraction leading to a distension of trabecular meshwork with subsequent reduction in outflow. and with trabecular meshwork contraction leading to the opposite effect. Smooth-muscle relaxing substances would therefore appear to be ideal candidates for glaucoma therapy with the dual goal of reducing intraocular pressure via the trabecular meshwork and of improving vascular perfusion of the optic nerve head. However, for such substances to effectively lower intraocular pressure, the effect on the ciliary muscle would have to he minimal. For this reason, more information is needed on the signalling processes involved in regulating trabecular meshwork and ciliary muscle contractility. This review attempts to outline current knowledge of signal transduction pathways leading to relaxation and contraction of ciliary muscle and trabecular meshwork. Pathways can be classified as involving or not involving changes of membrane voltage and of requiring or not requiring external calcium: possibly, other pathways exist. These different pathways involve different ion channels and isoforms of PKC and are expressed to a differing degree in ciliary muscle and trabecular meshwork, leading to differential responses when exposed to relaxing or contracting pharmacological agents. Some of these agents. like tyrosine kinase inhibitors and inhibitors of PKC. have been shown to relax trabecular meshwork while leaving ciliary muscle comparatively unaffected. This profile makes these substances appear as ideal drugs for simultaneously improving ocular outflow and retinal circulation, parameters that determine the time course of visual deterioration in glaucoma.
Animals↗
Mediation of calcium-independent contraction in trabecular meshwork through protein kinase C and rho-A.
PURPOSE: Inhibition of protein kinase C (PKC) and rho-kinase (ROCK) may represent a new way of influencing outflow facility through isolated relaxation of the trabecular meshwork (TM). This work was performed to investigate the existence of calcium-independent contraction in this smooth-muscle-like tissue and its modulation by targeting the rho-guanosine triphosphatase (GTPase)-mediated pathway. METHODS: Isometric tension measurements of bovine TM and ciliary muscle (CM) were performed. Intra- and extracellular calcium buffering was accomplished with EGTA and 1, 2-bis(2-aminophenoxy)-ethane-N,N:,N:,N:',N:'-tetra-acetic acid tetrakis/acetoxymethhyl ester (BAPTA-AM) followed by stimulation of PKC with phorbolester (PMA) or 4alpha-phorbol. Calcium-independent contraction was blocked using the highly specific ROCK inhibitor Y-27632. Western blot analysis and immunoprecipitation was performed using human TM cells. RESULTS: In TM, carbachol induced partial contraction under conditions of extracellular calcium depletion (22. 1% +/- 2.3% versus 100%, n = 9). The membrane-permeable calcium chelator BAPTA-AM completely blocked this response (1.1% +/- 1.4% versus 100%, n = 9). When calcium was completely blocked, PMA induced contraction in TM (16.7% +/- 5.9% versus 100%, n = 9) but not in CM (1.8% +/- 2.5% versus 100%, n = 6). The inactive PMA analogue 4alpha-phorbol did not induce contraction, indicating that activation of PKC is involved in this contractile response. The ROCK inhibitor Y-27632 completely blocked the calcium-independent PMA-induced contraction in TM. Western blot analysis and immunoprecipitation revealed the expression of the rho-A protein in human TM cells. CONCLUSIONS: The data indicate that contrary to CM, the TM features calcium-independent contractile mechanisms linked to rho-A and PKC isoforms that do not require calcium for activation. ROCK inhibitors may allow specific modulation of the TM to enhance outflow facility, thus lowering intraocular pressure.
Amides↗
The effects of the carbonic anhydrase inhibitors methazolamide, diclofenamide and dorzolamide on trabecular meshwork and ciliary muscle contractility.
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Animals↗
A pedigree of Leber's hereditary optic neuropathy with visual loss in childhood, primarily in girls.
BACKGROUND: Leber's hereditary optic neuropathy (LHON) mostly affects young males. In patients carrying one of the primary mutations the risk to develop LHON is 50% for males and 10% for females. We report a family with predominantly young girls affected. METHODS: In a family with 14 known maternal relatives (11 females, 3 males) 9 patients in 4 generations developed LHON. Eight of the 9 patients were females. Three affected females could be examined and followed. RESULTS: The only affected male showed the typical course of LHON with acute visual loss in both eyes (20/400-20/800) within 6 weeks at 20 years of age. Eight of 9 females developed signs of LHON. In these females acute visual loss occurred at about 10 years of age. Final visual acuity was about 20/200. Central or paracentral scotomata, color vision defects and delayed P100 latencies in the VEP were seen. Ophthalmoscopy showed hyperemic discs in the acute stage and optic atrophy in later stages. Molecular genetic analysis revealed the presence of the mtDNA ND4/np11778 mutation in this family. Specific clinical or additional molecular genetic risk factors could not be detected. CONCLUSION: Families with LHON may show considerable variations of the clinical course and the gender- or age-specific risk. We present a family with a high disease penetrance of 64% and a 2 times higher risk for young females than for males. Furthermore, early visual loss in this family is permanent.
Adult↗
The effects of protein kinase C on trabecular meshwork and ciliary muscle contractility.
PURPOSE: The possible role of protein kinase C (PKC) inhibitors in novel pressure-lowering drugs is currently under investigation. To gain further insight into regulation of contractility by PKC in trabecular meshwork (TM) and ciliary muscle (CM), the effects of various PKC inhibitors and activators were tested. METHODS: Isometric tension measurements of bovine TM and CM strips were performed. PKC was stimulated by phorbol ester and by the diacylglycerol analogue diC8. PKC blockade was accomplished using H7 and myristoilated PKC substrate (mPKC). Western blot analysis was used to identify specific PKC isoforms in human trabecular meshwork (HTM), human ciliary muscle (HCM), and bovine TM and CM. RESULTS: In tissues precontracted by carbachol PKC antagonist H7 led to a relaxation of TM (25+/-7.2 versus 100%; n = 8) with no effect on CM. mPKC substrate selectively blocks PKC. This substance led to relaxation of TM (32.8+/-7.4 versus 100%, n = 7), whereas CM was not affected. PMA at concentrations of 10(-6) M led to a slow contraction of both tissues that was more marked in TM. DiC8 and 4alpha-phorbol had no effect on contractility. Western blot analysis revealed expression of calcium-dependent PKC-alpha and calcium-independent PKC-epsilon isoforms in HTM and HCM. PKC-epsilon expression was more pronounced in HTM than in HCM. Similar PKC isoform expression was found in native bovine tissue. CONCLUSIONS: PKC isoforms show different tissue distributions in human and bovine TM and CM. Contractility differences exist in both tissues in response to PKC antagonists and agonists. The data indicate that PKC may be involved in regulation of aqueous humor outflow by the TM. Thus, inhibition of PKC may represent a new way of influencing outflow facility through isolated relaxation of TM.
1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
Lower Palaeolithic hunting spears from Germany.
Little is known about the organic component of Lower and Middle Palaeolithic technologies, particular with respect to wooden tools. Here I describe some wooden throwing spears about 400,000 years old that were discovered in 1995 at the Pleistocene site at Schöningen, Germany. They are thought to be the oldest complete hunting weapons so far discovered to have been used by humans. Found in association with stone tools and the butchered remains of more than ten horses, the spears strongly suggest that systematic hunting, involving foresight, planning and the use of appropriate technology, was part of the behavioural repertoire of pre-modern hominids. The use of sophisticated spears as early as the Middle Pleistocene may mean that many current theories on early human behaviour and culture must be revised.
Animals↗
Comparative analysis of vascular endothelial growth factor receptors on retinal and aortic vascular endothelial cells.
Ischemic eye disease often results in ocular neovascularization, presumably due to the elaboration of growth factors. Diabetic retinopathy is a classic example in which dramatic retinal neovascularization arises after ischemic retinal damage. The characterization of vascular endothelial growth factor (VEGF) as an angiogenic molecule whose expression is markedly induced by hypoxia makes it a promising candidate for mediating ischemic retinal neovascularization. Thus, we have characterized the structure, binding, and regulation of VEGF receptors in bovine retinal (BREC) and aortic endothelial cells (BAEC). VEGF stimulated a 2.1-fold increase in BREC number and DNA content at 0.6 nmol/l VEGF (P < 1 x 10(-7)). Scatchard binding analysis demonstrated specific high-affinity VEGF receptors on BREC with a Kd of 4.9 +/- 0.6 x 10(-11) mmol/l, similar to that observed for BAEC at 5.1 +/- 0.4 x 10(-11) mmol/l. BREC, however, possess 1.5 x 10(5) high-affinity receptors/cell, threefold more than BAEC (P < 0.003) and more than any cell type reported previously. 125I-VEGF affinity cross-linking revealed complexes at 220 and 170 kDa in BREC, but only a 220-kDa band of lesser intensity in BAEC. Cross-linking was displaceable in a dose-dependent manner by VEGF (P < 0.01) but not by other hormones. Hypoxia increased VEGF receptor number 50% in BREC without altering affinity. Antiphosphotyrosine immunoblotting showed VEGF-stimulated tyrosine autophosphorylation of VEGF receptor bands at 225 and 220 kDa and another band at 80 kDa within 1 min.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Vascular endothelial growth factor in ocular fluid of patients with diabetic retinopathy and other retinal disorders.
BACKGROUND: Retinal ischemia induces intraocular neovascularization, which often leads to glaucoma, vitreous hemorrhage, and retinal detachment, presumably by stimulating the release of angiogenic molecules. Vascular endothelial growth factor (VEGF) is an endothelial-cell-specific angiogenic factor whose production is increased by hypoxia. METHODS: We measured the concentration of VEGF in 210 specimens of ocular fluid obtained from 164 patients undergoing intraocular surgery, using both radioimmuno-assays and radioreceptor assays. Vitreous proliferative potential was measured with in vitro assays of the growth of retinal endothelial cells and with VEGF-neutralizing antibody. RESULTS: VEGF was detected in 69 of 136 ocular-fluid samples from patients with diabetic retinopathy, 29 of 38 samples from patients with neovascularization of the iris, and 3 of 4 samples from patients with ischemic occlusion of the central retinal vein, as compared with 2 of 31 samples from patients with no neovascular disorders (P < 0.001, P < 0.001, and P = 0.006, respectively). The mean (+/- SD) VEGF concentration in 70 samples of ocular fluid from patients with active proliferative diabetic retinopathy (3.6 +/- 6.3 ng per milliliter) was higher than that in 25 samples from patients with nonproliferative diabetic retinopathy (0.1 +/- 0.1 ng per milliliter, P = 0.008), 41 samples from patients with quiescent proliferative diabetic retinopathy (0.2 +/- 0.6 ng per milliliter, P < 0.001), or 31 samples from nondiabetic patients (0.1 +/- 0.2 ng per milliliter, P = 0.003). Concentrations of VEGF in vitreous fluid (8.8 +/- 9.9 ng per milliliter) were higher than those in aqueous fluid (5.6 +/- 8.6 ng per milliliter, P = 0.033) in all 10 pairs of samples obtained simultaneously from the same patient; VEGF concentrations in vitreous fluid declined after successful laser photocoagulation. VEGF stimulated the growth of retinal endothelial cells in vitro, as did vitreous fluid containing measurable VEGF. Stimulation was inhibited by VEGF-neutralizing antibodies. CONCLUSIONS: Our data suggest that VEGF plays a major part in mediating active intraocular neovascularization in patients with ischemic retinal diseases, such as diabetic retinopathy and retinal-vein occlusion.
Adolescent↗
Effect of elevated glucose concentration on membrane voltage regulation in retinal capillary pericytes.
The influence of elevated glucose concentration on resting membrane voltage, electrogenic Na(+)-K(+)-ATPase, and ATP-sensitive potassium channels (KATP channels) was studied in cultured bovine retinal capillary pericytes using conventional microelectrodes. The resting membrane voltage in cells grown in medium containing 5 mM glucose (control) averaged -27 +/- 1.2 mV (mean +/- SE, n = 26) and was not different from cells grown in medium containing 22.5 mM glucose (-26 1.2 mV, n = 26). Addition of ouabain (10(-4) M), a specific inhibitor of the Na(+)-K(+)-ATPase, depolarized the membrane potential by 3.6 +/- 0.4 mV (n = 10) in cells grown under control conditions and 0.7 +/- 0.2 mV (n = 6) in cells grown under elevated glucose conditions. Thus, electrogenic activity of the Na(+)-K(+)-ATPase was significantly (P < 0.0001) reduced to 19% compared with control conditions. Electrogenic Na(+)-K(+)-ATPase activity could be partially restored (ouabain-induced depolarization delta V = 2.0 +/- 0.2 mV, n = 6) in cells grown with high glucose in the presence of the aldose reductase inhibitor tolrestat (10(-5) M). The potassium channel opener Hoe 234 (10(-6) M) induced membrane potential hyperpolarization in control cells (delta V = 7.3 +/- 1.2 mV, n = 13), which could be completely inhibited by the KATP channel blocker glibenclamide (10(-7) M, n = 5). This indicates that pericytes possess KATP channels. The effect of KATP channels on membrane voltage was not significantly changed (P = 0.16) in cells cultured under high-glucose conditions (delta V = 9.6 +/- 2.0 mV, n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Insulin-induced hyperpolarization in retinal capillary pericytes.
PURPOSE: This study investigated the mechanism of insulin-induced membrane voltage hyperpolarization in retinal capillary pericytes, which possess electrical membrane properties typical for smooth muscle cells and are supposed to regulate retinal microcirculation by a contractile mechanism. METHODS: The mechanism of insulin-induced hyperpolarization was studied in cultured bovine retinal capillary pericytes using conventional microelectrodes. RESULTS: Resting voltage averaged -28 +/- 0.9 mV (mean +/- SEM, n = 45). Insulin (10(-9) to 10(-7) mol/l) induced a slow hyperpolarization in a dose-dependent fashion. Voltage change (delta V) was -3.1 +/- 0.4 mV (n = 14, P < 0.0001, = control) with an insulin concentration of 10(-8) mol/l. Blockade of potassium channels with Ba2+ (5 mmol/l) completely abolished the hyperpolarizing effect of insulin (n = 5). Apamin (10(-9) mol/l), a blocker of low-conductance Ca(2+)-activated potassium channels, also completely inhibited the insulin-induced hyperpolarization (n = 4). Blocking ATP-sensitive potassium channels with glibenclamide (10(-7) mol/l) did not reduce the hyperpolarizing action of insulin (delta V = -2.2 +/- 0.4 mV, n = 5, P = 0.29). Equivalent hyperpolarizations were recorded when insulin was added in the presence of ouabain (10(-4) mol/l) to inhibit the electrogenic Na+/-/K+/-ATPase (delta V = -3.5 +/- 1.0 mV, n = 4, P = 0.68). When pericytes were grown for 3 days in culture medium with elevated glucose concentrations (22.5 mmol/l), the resting membrane voltage and the insulin-induced hyperpolarization were not significantly altered. CONCLUSION: Insulin hyperpolarizes the membrane voltage of retinal pericytes probably mediated by activation of apamin-sensitive Ca(2+)-activated potassium channels. Therefore, hormonal modulation of membrane voltage by insulin might be an important factor in the regulation of pericyte contractility and retinal microcirculation under physiological conditions and in diabetes mellitus.
Adenosine Triphosphate↗
[Residues of organochlorine compounds in plant drugs. 1. Gas chromatographic determination of residues of organochlorine insecticides].
A method for the identification and determination of HCH-and DDT-isomers and their respective metabolites in vegetable drugs is presented. The plant material is extracted with hexane in a Soxhlet apparatus in the presence of silicagel and sodium sulfate. For removing interfering endogenous plant constituents a Celite oleum column cleanup and usually and acetonitrile partitioning to follow are necessary. A mixed stationary phase OV-17/QF-1 has proved effective for the gc separation on packed columns. 3H-ECD is used for detection. For the quantitative determination by using an external standard the peak height measurement is recommended. Recoveries of all insecticides were in the order of 70-105% with coefficients of variation between 6 and 20%. To ensure the results the alkaline treatment and oxidation of extracts are proposed.
Chromatography, Gas↗