Membrane and communication properties of tissue cultured human lens epithelial cells

Explant cultures were established from capsule/epithelium preparations from both normal and cataractous lenses to investigate properties of human lens epithelial cells. The cultured cells were found to have similar membrane potentials to whole human lenses and isolated epithelia, and similar free ionic concentrations of potassium, sodium, and calcium (131 mM, 17 mM and 0.8 microM respectively) to whole human lenses. The free ionic concentrations were measured in both cases using neutral resin-filled electrodes. Cellular communication was investigated using electrical (two internal microelectrodes) and dye injection techniques. The electrical resistance of a confluent cell monolayer was approximately 4 M omega when the voltage measuring and current passing microelectrodes were in neighbouring cells or several cell diameters apart. Additionally, Lucifer Yellow dye injected into one cell spread rapidly over a wide area of cells. The cells thus appear to be extremely well coupled. Electrical communication could be disrupted by internal acidification (following exposure to 100% CO2), exposure to 1 mM octanol and by membrane depolarization. In the latter case the blockade was only partial. All uncoupling methods proved to be reversible. The diffusion of Lucifer Yellow dye was also inhibited by internal acidification and exposure to octanol. The sensitivity of both dye and electrical coupling to internal acidification and exposure to octanol is similar to that observed in hepatocytes and other tissues, whereas the effect on cell communication induced by changing the resting potential appears to occur only in a few cell types such as those of embryonic origin.

Efflux of chloride from the rat lens: influence of membrane potential and intracellular acidification

The efflux of 36C1 from perifused rat lenses consisted of two components: a fast (extracellular) component and a slow (cellular) component. The 36C1 efflux rate constant of the cellular component was 5.7 X 10(-3) min-1. The 36C1- efflux was sensitive to changes in lens potential induced by treatment with high-K+ solutions. The decrease in the 36C1- efflux rate constant caused by high-K+ solutions was consistent with the Goldman model, indicating that, under normal conditions, the majority of the 36C1 efflux is by diffusion. The 36C1- efflux rate constant corresponds to a C1 permeability of 1.3 X 10(8) ms 1. The C1- channel inhibitor anthracene-9-carboxylate (A-9-C), however, caused a relatively small reduction in the efflux rate constant. The anion-exchange inhibitor 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonate (SITS) has little effect on the 36C1 efflux under control conditions. Intracellular acidification, induced by pre-treatment with NH1+, leads to a rapid stimulation of 36C1- efflux. This increased 36C1- efflux is blocked by SITS. Thus, it appears that at low intracellular pH (pH), a normally quiescent, SITS-sensitive, anion-exchange mechanism is activated. The possible role of this exchange mechanism in regulating pH, is discussed.

p-chloro-mercuriphenyl sulphonate activates a quinine-sensitive potassium conductance in frog lens

1. The effects of the sulphydryl-complexing reagent p-chloro-mercuriphenyl sulphonate (pCMPS) on membrane voltage and electrical conductance were studied on the isolated frog lens. 2. At low concentrations (0.1-50 microM) pCMPS induced a rapid and graded hyperpolarization of the lens membrane potential which saturated at -97 mV. 3. The lens conductance also showed a graded increase, but the initial changes were apparent only at concentrations above 1 microM. 4. Decreasing the external potassium concentration from 2.5 to 0.5 mM had little effect on the membrane potential in the absence of pCMPS, but increased the voltage from -97 to -110 mV when pCMPS was present. 5. Quinine (300 microM) had no effect when added in control solution, but depolarized the membrane potential and decreased the conductance when added to a pCMPS-treated preparation. 6. These data suggest that pCMPS activates voltage-sensitive potassium channels that are quiescent at the frog resting potential in control solution. 7. At pCMPS concentrations greater than or equal to 100 microM, the initial hyperpolarization is followed by a marked but slow depolarization of the membrane potential and a further increase in lens conductance. These data suggest that non-specific cation channels are activated in this case. 8. Cysteine (5 mM) added to a pCMPS-treated lens leads to a rapid recovery of membrane potential and conductance to near their resting values whether the lens had previously been exposed to low or high concentrations of pCMPS. 9. All of these changes in lens voltage and conductance occurred without apparent alteration in the lens internal sulphydryl content.

Oxidative cross-linking of fodrin parallels a membrane conductance increase in the mammalian lens

An oxidative cross-linking of the lens spectrin-like protein fodrin was induced by incubating WKY-rat lenses in the presence of the SH-reagent diamide. The oxidation of fodrin was paralleled by an increase in lens membrane conductance. The time relationship between these two events as well as the reversibility of both, achieved by incubating the lens in the presence of dithiothreitol, indicate that normal permeability characteristics of the lens membranes require the integrity of the membrane attached cytoskeleton.

Membrane and junctional properties of the isolated frog lens epithelium

The isolated frog lens epithelium can be maintained intact in both appearance and electrical properties for more than 24 hours. The mean resting membrane potential was -80 mV and the cells were depolarized by both high potassium and low calcium Ringer's solution in a manner very similar to that of the whole lens. The epithelial cells were found to be well coupled using both electrical and dye-injection techniques. Electrical coupling was measured using separate current-injection and voltage-measuring electrodes and the relationship between the induced voltage and distance from the current-passing electrode could be well fitted by a Bessel Function solution to the cable equation. The values obtained from the fit for the membrane and internal resistances were 1.95 omega m2 and 25 omega m, respectively. Exposure to octanol (500 microM) or low external Ca2+ (less than 1 microM) failed to disrupt significantly the intercellular flow of current. There was evidence to suggest that raised intracellular calcium does, however, uncouple the cells. Dye coupling was investigated by microinjecting Lucifer Yellow CH into single epithelial cells. Diffusion into surrounding cells was rapid and, in control medium, occurred in a radially symmetrical manner. In contrast to the electrical coupling data, dye transfer appeared to be blocked by exposure to 500 microM octanol and was severely restricted on perfusing with low external calcium. Differences between the electrical and dye-coupling experiments indicate either that there are two types of junction within the cell and only the larger type, permeable to Lucifer Yellow, is capable of being uncoupled or that there is only one large type of junction which can be partially closed by uncoupling agents.

The influence of pH on membrane conductance and intercellular resistance in the rat lens

1. The conductance of the rat lens was measured using a two-internal-microelectrode technique. The voltage response to a step of current consisted of two components arising from bulk and membrane resistance respectively. 2. The potassium permeability was calculated by applying Goldman theory to 86Rb+ efflux data. 3. The internal pH (pHi) and internal free calcium (pCai) were measured directly using single- and double-barrelled ion-sensitive microelectrodes. 4. Lens pHi was 6.9 in control solution (external pH, pHo = 7.3) and was reduced on lowering pHo. The presence of propionate or 100% CO2 in the external solution accentuated this effect. 5. Internal acidification was accompanied by a depolarization of membrane potential, an increase in membrane and cell-to-cell resistance and a decrease in potassium permeability. The acidification had no effect on pCai. 6. The intracellular pH was increased by perifusing with trimethylamine or NH4Cl. Both treatments induced a membrane depolarization with little change in potassium permeability. Subsequent removal of NH4Cl led to a sustained decrease in pHi. 7. In every case where pHi decreased, the changes in membrane potential and conductance could be explained largely on the basis of a decrease in potassium permeability. The concomitant increase in cell-to-cell resistance was less pronounced and probably insufficient to uncouple the lens system.

Amino acid transport and protein synthesis in human normal and cataractous lenses

The ability of normal and cataractous human lenses to accumulate amino acids and synthesize proteins was studied under organ culture conditions. As expected, normal lenses regulate their internal ion levels, accumulate amino acids against a concentration gradient, and continue to synthesize proteins even in advanced age (greater than 60 yrs). The cataractous lenses fell basically into two groups. Those with a low internal sodium and calcium content behaved in a similar manner to normal lenses, but cataractous lenses with high sodium and calcium contents showed a markedly reduced ability to accumulate amino acid and synthesized less low molecular weight protein. They incorporated, however, a much higher proportion of labelled amino acid into high molecular weight protein. While sodium appears to be the ion involved in changes in amino acid accumulation, calcium seems to play a critical role in the disturbance of lens protein synthesis and also protein-protein interaction. Both loss of protein and accumulation of high molecular weight aggregates may be due to modifications induced by the calcium-activated protease, calpain. None of the changes appeared to be correlated with increasing nuclear brunescence.

Colchicine myopathy and neuropathy

Although colchicine has been used for centuries, its neuromuscular toxicity in humans is largely unrecognized. In this report we describe a characteristic syndrome of myopathy and neuropathy and present 12 new cases of the condition. Colchicine myopathy may occur in patients with gout who take customary doses of the drug but who have elevated plasma drug levels because of altered renal function. It usually presents with proximal weakness and always presents with elevation of serum creatine kinase; both features remit within three to four weeks after the drug is discontinued. The accompanying axonal polyneuropathy is mild and resolves slowly. Electromyography of proximal muscles shows a myopathy that is marked by abnormal spontaneous activity. Because of these features, colchicine myoneuropathy is usually misdiagnosed initially, either as probable polymyositis or as uremic neuropathy. The myopathy is vacuolar, marked by accumulation of lysosomes and autophagic vacuoles unrelated to necrosis or to the mild denervation in distal muscles. The morphologic changes in muscle suggest that the pathogenesis involves disruption of a microtubule-dependent cytoskeletal network that interacts with lysosomes. Correct diagnosis may save patients with this disorder from inappropriate therapy.

Membrane conductance and potassium permeability of the rat lens

The membrane potential, electrical impedance and 86Rb+ efflux rate constants were measured in the rat lens perifused at 35 degrees C. The membrane conductance was obtained from the difference between the magnitude of the impedance at low (less than 0.1 Hz) and high (greater than 100 Hz) frequencies. Values of the rubidium permeability coefficients (PRb) were obtained from the rate constant and potential data. The values for the membrane potential and conductance in control solution (5 mM potassium) were -69.6 mV and 5.5 X 10(-4) S respectively, while the computed permeability was 2.9 X 10(-8) m.s-1. On perifusing with 35 mM potassium, the membrane depolarized by 25 mV and the conductance and rubidium permeability increased considerably. These increases could be blocked by quinine (0.3 mM), tetraethylammonium (30 mM) and 4-aminopyridine (10 mM). The latter agent was more effective at alkaline pH (8.3). It is suggested that there are voltage-gated potassium channels that are inhibited by these three agents. After the initial depolarization in high potassium, there was little further change in membrane potential with any of the inhibitors. All three agents, however, produced a marked depolarization when applied in control solution. This was accompanied by a decrease in conductance and rubidium permeability, suggesting that, in the rat lens, some voltage-gated potassium channels are activated at the resting potential.

Calcium-induced opacification and loss of protein in the organ-cultured bovine lens

A long-term system of organ culture for bovine lenses was used to investigate the effect of osmotic stress on lens opacification and crystallin loss. Lenses were pre-incubated in control medium containing L-[U-14C]tyrosine so that labelled crystallins were produced. The fate of these crystallins was studied in relation to two forms of osmotic stress. The addition of either ouabain or EGTA to the medium induced severe osmotic swelling and disturbance of the lens monovalent cation balance, but only the former treatment was followed by an increase in lens calcium. The changes due to osmotic stress were accompanied by loss of transparency and protein only in the lenses with increased calcium. Both opacification and increased calcium were found largely to be confined to the outer cortical fibres. Protein loss increased with time as lens calcium continued to increase. The protein recovered from the incubation medium was characterized by gel filtration and immunological techniques. The first protein detected was beta L-crystallin, and this formed the major part of the lost protein throughout, although alpha- and gamma-crystallins were detected at a later stage. Increased calcium also resulted in a change in the susceptibility of the crystallins to aggregation, since there was an increase in [14C]tyrosine incorporated into the lens high-molecular-weight (HM) fraction after exposure to ouabain, but not after exposure to EGTA. The relevance of these findings to human cataract is discussed.

Dorsal horn opiate administration attenuates the perceived intensity of noxious heat stimulation in behaving monkey

In monkeys trained to detect and discriminate noxious heat stimuli, morphine microinjected into the medullary dorsal horn attenuated the perceived intensity of noxious heat in a dose- and stimulus-dependent fashion. These data demonstrate a pharmacologically specific effect of opiates on the sensory intensity component of pain at the earliest central relay pathway transmitting noxious information.

Membrane permeability characteristics of perfused human senile cataractous lenses

Human cataractous lenses were removed by the cryoprobe technique and were maintained for up to 24 hr in a solution of similar ionic composition to human aqueous humour. The bimodal distribution of internal sodium concentrations was similar to that previously reported for unincubated human lenses. Lenses with lower total and free sodium contents had relatively higher membrane potentials and they lost 86Rb at a slower rate than lenses with high internal sodium. The 86Rb efflux in these lenses was stimulated four-fold by removing external calcium. The efflux was reduced by increasing external calcium, but was increased during a small (60 mosmol) hyperosmotic shock. A similar hyperosmotic shock also surprisingly increased 86Rb efflux. Lenses with increasing internal sodium (and calcium) levels showed an increasing rate of loss of 86Rb and the stimulation by calcium removal was progressively diminished. The efflux from lenses with disturbed ion levels was also relatively insensitive to changes in external osmolarity and to increasing external potassium. Lenses with raised sodium concentrations also had an increased inulin space. Frog, rat and rabbit lenses were also exposed to the same range of stimuli and only frog lenses responded to the low calcium solution with more than a four-fold increase in efflux rate. Although only a two- to four-fold increase in efflux rate was obtained from rabbit lenses exposed to Ca-free conditions, this was the only type of animal lens so far tested that, like the human lens, responded to both hyperosmotic and isosmotic shocks with an increase in efflux rate. All three species of mammalian lenses responded with an increase in efflux rate when exposed to a hyperosmotic test solution while in the frog, the efflux rate from the lens decreased. The glucose efflux from human cataractous lenses was inhibited by cytochalasin B in a similar manner to the efflux from rat and frog lenses. It was concluded, therefore, that the cryoprobed human lens can be kept for a limited period in a relative simple artificial aqueous humour solution. The potassium permeability characteristics of low sodium cataracts remained relatively intact and showed a unique response (relative to lenses from other animals) when exposed to various stimuli that are known to be potentially cataractogenic.

Operantly conditioned running: effects on brain catecholamine concentrations and receptor densities in the rat

It was hypothesized that endurance exercise results in an alteration in the brain monoamine systems. Rats were trained to run for food reinforcement on a variable ratio schedule in running wheels. Yoked control rats were also allowed to run but were not specifically reinforced for running. The animals ran 5 days per week for 8 weeks and were sacrificed 48 hours after the last endurance training session. The brains were assayed for norepinephrine and dopamine concentrations and beta-adrenergic (3H-dihydroalprenolol binding) and dopaminergic (3H-spiroperidol binding) receptor densities. Changes in norepinephrine concentration and beta-adrenergic receptor densities were not significantly different between reinforced running and yoked control groups. Dopamine concentrations were significantly higher while dopamine receptor densities were significantly lower in the reinforced running group. These results suggest that chronic running elevates dopamine secretion and consequently produces a compensatory down-regulation of dopaminergic receptor sites. The relationship of these changes to motor activity and to the antidepressant effects of exercise are discussed.

Amiodarone: risk factors for recurrence of symptomatic ventricular tachycardia identified at electrophysiologic study

Ventricular tachycardia induced by programmed electrical stimulation during amiodarone therapy often does not preclude a good clinical response. The purpose of this study was to determine whether use of discriminant analysis could distinguish patients who remained asymptomatic from those who subsequently developed symptomatic ventricular tachycardia or cardiac arrest. Studies were performed in 37 patients with sustained ventricular tachycardia who still had ventricular tachycardia induced during programmed electrical stimulation during amiodarone therapy. The mean follow-up time was 14.1 +/- 1.3 months (+/- SEM). Twenty-three patients remained asymptomatic, whereas 14 patients had symptomatic recurrence of their ventricular tachycardia. In patients with recurrence of arrhythmia compared with asymptomatic patients, administration of amiodarone caused a longer ventricular effective refractory period (296 +/- 8 versus 271 +/- 7 ms, p less than 0.05) and a greater change in corrected QT [QTc] interval (90 +/- 18 versus 44 +/- 9 ms, p less than 0.02), but no difference in the decrease in premature ventricular complexes after treatment with amiodarone. During amiodarone therapy, nonbundle branch reentrant repetitive ventricular responses were induced by a single ventricular extrastimulus during sinus rhythm in 9 of 14 patients with recurrent arrhythmias compared with 2 of 21 asymptomatic patients (p = 0.001). Also, less aggressive pacing techniques were required to induce ventricular tachycardia in 9 of 14 symptomatic patients compared with 4 of 23 asymptomatic patients (p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adverse effect of smoking on the hyperaemic response in diabetic patients and control subjects

In order to determine whether smoking had an adverse effect on the hyperaemic response, as measured by transcutaneous oximetry, matched groups of insulin-dependent diabetic smokers and non-smokers were compared both with each other and with similar matched groups of non-diabetic control subjects. The hyperaemic response was also measured immediately, 1 hour and 24 hours after smoking a cigarette in five control subjects who smoked. The hyperaemic response was significantly lower in the diabetic smokers compared with the diabetic non-smokers (p = 0.008) and in the control smokers compared with the control non-smokers (p = 0.011). No other significant differences were found. In the five subjects studied at intervals after smoking the responses were variable and inconsistent. Smoking modifies the hyperaemic response and this must be taken into account in any investigation using such measurements.

Characterization of a cation channel on the apical surface of the frog lens epithelium

The properties of a single conductance pathway of the apical (fibre-facing) surface of the frog lens epithelium are reported. Using the patch-clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981), the most common single-channel currents had an amplitude of 1.9 pA, the mean open time 2.1 ms and a conductance of 25 pS. One open-state time constant (to = 3.3 ms) and two closed-state time constants (tau c1 = 0.9 ms, tau c2 = 23.1 ms) were resolved. The channel current and the mean open time were both increased when Ca2+ was removed from the external solution and the open time distribution was no longer fitted by a single exponential. Multiple-channel events in cell-attached patches containing two or more identical channels were distributed in a binomial fashion and the probability that an individual channel was open, obtained by fitting the binomial distribution, was 0.039. The channel was found to have a Na+:K+ selectivity ratio of 3:1. When Ca2+ was removed from the pipette solution the probability that an individual channel was open increased to 0.137 and the Na+:K+ selectivity ratio increased to 4:1. Channel activity was observed in the presence of tetrodotoxin (10(-6) M) in the bathing medium and the pipette solution but was abolished by internal perfusion of the patch pipette with 0.5 x 10(-4) M amiloride. this apical conductance pathway is identified as an amiloride-sensitive cation channel. These channels are clustered in groups on the apical membrane, spontaneously active at the resting potential and with the possibility of altering their Na+:K+ selectivity. They represent a distinct type of channel, that differ from nerve and muscle Na+ channels in their manner of activation, but do share some common features with both Na+ and Ca2+ channels in excitable cells.

Direct measurement of pH in the rat lens by ion-sensitive microelectrodes

The resting pH of the rat lens was determined using H+-sensitive liquid membrane microelectrodes and found to be 6.89 when measured in a perifusing solution of pH 7.20. The pH of the rat vitreous humour was also measured and was found to be 7.25. Attempts were made to perturb the lens pH by varying the pH of the perifusate. In the presence of alkaline solutions, the lens was able to maintain its resting pH and membrane potential but, upon perfusion with a more acidic solution, the lenticular pH equilibrated with the pH of the bathing solution and the potential depolarized. The internal pH could be manipulated independently of the external pH by perfusing the lens with Ringer solution containing 20 mM ammonium chloride. The ammonium chloride induced a rapid alkalinization and the return to control solution caused a fall in pH to below the normal resting level. The biphasic pH response to ammonium chloride was accompanied by changes in lens transparency and membrane potential.

Influence of external calcium and glucose on internal total and ionized calcium in the rat lens

Free calcium in the rat lens, measured by ion-sensitive electrodes, is 1.8 microM while the total, measured by atomic absorption, is of the order of 600 microM. The measured free calcium concentration (pCa) varies with the depth below the surface. It is lowest in the region 100-400 micron below the capsule and again in the nucleus, while the intervening perinuclear cortex has a relatively high free calcium. In young rats (less than 16 weeks) the free calcium in the posterior and anterior cortical regions is the same, while in the older lenses the free calcium is lower in the anterior and the regional variation is greater. Rat lenses incubated in a medium of similar ionic composition to aqueous humour for 15-24 h maintained a low level of free calcium. The maintenance of low internal calcium (both free and total) was dependent on external glucose and on removing glucose the intracellular free calcium increased from 5 to 15 microM while the total calcium increased from 600 to over 1000 microM. Following incubation in high calcium (10 mM), the free and total calcium increased to 40 and 3000 microM respectively. Omitting glucose from the high-calcium solution led to a further increase in both free and total calcium to 400 and 10000 microM respectively. The incubated control lenses maintained their normal sodium and potassium levels and resting potential, while removing glucose gave rise to an increase in sodium, a decrease in potassium and a depolarization of the membrane potential. Increasing external calcium also depolarized the membrane potential, but there was no change in internal sodium and potassium.(ABSTRACT TRUNCATED AT 250 WORDS)

Aqueous humour glucose concentration in cataract patients and its effect on the lens

The glucose concentrations of the blood plasma and aqueous humour were measured in 56 cataract patients. The sodium concentration and colour of the lenses were determined after extraction. The mean plasma and aqueous glucose levels were 5.8 and 3.2 mM respectively in non-diabetic patients, while the values for diabetics were 14.2 and 7.8 mM. The sodium concentration of the lenses from non-diabetic patients appeared to consist of two distributions around 30 and 170 mM, corresponding to nuclear and cortical cataracts respectively. Only two lenses from the non-diabetic patients had sodium concentrations in the range 60-120 mM. In diabetic patients, however, 80% of the extracted lenses had sodium concentrations in this intermediate range. The data indicate that the osmotic stresses induced in the lenses of diabetic and non-diabetic patients are different. The diabetic lenses were also distributed in the middle range when nuclear colour was graded on a scale from I to V, while normal lenses were again normally distributed at either end of the scale.

Effect of 8-methoxypsoralen on rat lens cations, membrane potential and protein levels

Systemic application of 8-methoxypsoralen to rats, followed by u.v.-irradiation, induces a minor change in the lens membrane potential after one week, and by this time marked histological changes have already occurred. Alterations in lens sodium and potassium concentrations followed these early changes and coincided with the appearance of small light-scattering vacuoles when the lenses were examined in vivo with a slit lamp. Dramatic changes in the dry weight, soluble protein and calcium content of the lenses were apparent only after eight weeks from the start of treatment, and these changes coincided with the appearance of very large vacuoles in slit-lamp examinations of the eye.