A teflon culture dish for high-magnification microscopy and measurements in single cells

A simple method for monitoring changes in cell height using fluorescent microbeads and an Ussing-type chamber for the inverted microscope

In this study, we report two developments for studies of ion transport in cultured epithelial cells. First, a convenient method is presented for measuring apparent cell height using fluorescent microbeads as high-contrast landmarks of the apical and basal cell surfaces. The apparent cell height is then used as an indicator to monitor the time course of changes in cell volume in response to osmotic perturbations. Second, an Ussing-type chamber design for the inverted fluorescence microscope is presented, which allows determination of transepithelial electrical properties. Using these two methods, we obtained simultaneous measurements of cell height and transepithelial electrical parameters for cultured renal (A6) epithelium. Cell height was measured by alternately focusing the microscope between microbeads marking the apical and basal surfaces. The distance between these two surfaces was measured electrically from the voltage output of a potentiometer that was mechanically coupled to the fine-focusing knob of the microscope. Following decreases in the bathing solution osmolality, the cell height and transepithelial Na+ transport rate (measured as short-circuit current, ISC) increased. The increase in cell height preceded changes in ISC by several minutes, suggesting a lack of direct linkage between changes in cell volume and transepithelial Na+ transport. Both the fluorescent microbead cell height method and the Ussing-type chamber can be used in conjunction with patch-clamp techniques, intracellular microelectrode impalements, or fluorescent probes of intracellular composition. Therefore, this system may be advantageous for studies of epithelial cell volume and channel regulation.

Characterization of Ca2+ transients induced by intracellular photorelease of InsP3 in mouse ovarian oocytes

Ca2+ transients (measured with Fluo-3) were induced in single mouse ovarian oocytes by photolytic liberation of InsP3. The time course of cytosolic Ca2+ changes induced in this way is composed of distinct phases: upstroke, fast decline, slow declining plateau and fast decline to rest level. All the phases reflect mainly intracellular redistributions of the ion and not influx, since they are not strongly dependent on external Ca2+ or on changes in transmembrane potential. Often sustained Ca2+ oscillations followed the first InsP3-induced Ca2+ transient. These persisted for several minutes in the absence of external Ca2+. The initial rate of Ca2+ rise and the delay between the InsP3 stimulus and Ca2+ upstroke are correlated with the amount of liberated InsP3. A second InsP3 stimulation, applied during the plateau, causes only small Ca2+ elevations, lacking the upstroke phase. A second, full sized, transient could be elicited only after a complete return to the basal level. Vanadate, applied intracellularly, appeared to inhibit the re-uptake phase into the stores, stabilizing the plateau level. The present observations suggest that in mouse oocytes the InsP3-sensitive stores provide only a small and graded Ca2+ release which may then act as a trigger for a more substantial Ca(2+)-induced Ca2+ release (CICR) process.

Regulation of movement speed by intracellular pH during Dictyostelium discoideum chemotaxis

Evidence is presented that the chemoattractant-induced cytoplasmic alkalinization in the cellular slime mold Dictyostelium discoideum is essential in regulating locomotion speed during chemotaxis. Intracellular pH was manipulated with weak bases, weak acids, and proton-pump inhibition. Speed of locomotion of individual cells was measured during random and chemotactic movement. We found that (i) an increase of cytoplasmic pH increases the speed of randomly moving cells and (ii) the chemoattractant-induced rise in intracellular pH is essential for the increase in directed locomotion speed upon chemotactic stimulation. In addition, our experiments support the hypothesis that ammonia plays a key role in the thermo- and phototaxis of migrating slugs by increasing the locomotion speed of individual cells through changes in intracellular pH.

High-conductance anion channels in embryonic chick osteogenic cells

Patch-clamp measurements done on excised membrane patches obtained from 1-5 day cultured embryonic chick osteoblasts, osteocytes, and periosteal fibroblasts revealed the existence of a high-conductance anion channel: 371 +/- 63 pS when measured under symmetrical 158 mM Cl- conditions. The channel frequently displayed subconductance levels. The ion selectivity of the channel expressed as the (an)ion to chloride permeability ratio was as follows: Cl- (1.0) greater than methylsulfate- (0.71) greater than gluconate- (0.25) greater than glutamate- (0.17) greater than Na+ = K+ (0.10). In addition, the channel had a significant permeability for inorganic phosphate ions. The channel was found in about 1% of the cell-attached patches, which indicates that the channel is under the control of as yet unknown intracellular factors. Once activated by patch excision, the channel was voltage dependent and active at potentials close to 0 mV. At potentials outside the range of +/- 10 mV channel activity decreased. This process proceeded faster at increasing membrane potentials of either polarity. Returning to potentials close to 0 mV caused reopening of the channels within seconds if the preceding voltage step led to complete closure of the channels. Channel activity did not depend noticeably on intracellular and extracellular CA2+ ions. The channel is not unique to (chick) osteogenic cells but has been demonstrated in excised patches obtained from excitable and other nonexcitable cells. Although its presence in a wide variety of cell types suggests that the channel plays a general role in as yet unknown cell physiologic processes, the channel may also have specific functions in osteogenic cells, for example providing a pathway for phosphate ions during mineralization.

Identification of Ca(2+)-activated K+ channels in cells of embryonic chick osteoblast cultures

Primary cultures of embryonic chick osteoblasts consist of a heterogeneous cell population. Patch clamp measurements were done on 1- to 5-day-old osteoblasts, osteocytes, fibroblastlike cells, and cells that could not be classified on morphologic criteria. The measurements showed the omnipresence of depolarization-activated high-conductance channels in cell-attached patches. The whole-cell experiments showed an outward rectifying conductance activating at positive membrane potentials. Channels underlying the latter conductance were found to be K+ conducting in outside-out membrane patches. The activation potential of the outward rectifying K+ conductance shifted to negative membrane potentials upon increasing the intracellular Ca2+ concentration within the range of 10(-8)-10(-3.2) M. The same happened with the activation potential of the K+ channels found in outside-out patches. Finally, inside-out patch experiments directly demonstrated the dependency of the activation potential of K+ channels on Ca2+ ions. Thus the identity and main characteristics of Ca2(+)-activated K+ channels expressed by the various cell types present in chick osteoblast cultures have now been established. Decreased input resistances were found in cells of cultures more than 2 days old. This is consistent with the establishment of electrical coupling between the cells. Functions in which Ca2(+)-activated K+ channels could play a role are discussed.

Gangliosides normalize distorted single-cell intracellular free Ca2+ dynamics after toxic doses of glutamate in cerebellar granule cells

Glutamate-induced delayed neurotoxicity after abusive and paroxismal activation of its receptors has been proposed to depend upon a sustained increase in intracellular free Ca2+ [( Ca2+]i). To elucidate the temporal and causal relationship between glutamate-induced changes in [Ca2+]i and neuronal death, we simultaneously studied the dynamics of [Ca2+]i changes in single neurons with the acetoxymethyl ester of fura-2 and the cell viability by imaging the nuclear penetration of propidium iodide. The main difference between toxic (50 microM) and nontoxic (5 microM) doses of glutamate is the lack of regulation in [Ca2+]i 20 min after glutamate is removed. This protracted rise in [Ca2+]i in a single cell is correlated with (r = 0.87, P less than 0.01, Spearman's test), and consequently predictive of, the time of appearance of neuronal death, as measured by propidium iodide fluorescence. In addition, the glutamate receptor antagonists dibenzocyclohepteneimine (MK-801) and 3,3-(2-carboxypiperazine-4-yl)propyl 1-phosphate reduce the acute increase of [Ca2+]i induced by glutamate but fail to revert the protracted increase of [Ca2+]i, elicited by toxic doses of glutamate. In contrast, the ganglioside GM1 and the semisynthetic lysoGM1 with N-acetylsphingosine (LIGA-4) and lysoGM1 with N-dichloroacetylsphingosine (LIGA-20) failed to change the immediate rise of [Ca2+]i elicited by glutamate but prevented the protracted increase in [Ca2+]i after toxic doses of glutamate. Voltage-dependent Ca2+ channel blockers (nifedipine, etc.) did not change the initial or protracted responses to glutamate.

Thyroid status and beta-agonistic effects on cytosolic calcium concentrations in single rat cardiac myocytes activated by electrical stimulation or high-K+ depolarization

The effects of the thyroid status on the cytosolic free Ca2+ concentration ([Ca2+]i) in single cardiomyocytes were studied at rest and during contraction. The mean resting [Ca2+]i increased significantly from the hypothyroid (45 +/- 4 nM) through the euthyroid (69 +/- 12 nM) to the hyperthyroid condition (80 +/- 11 nM) at extracellular Ca2+ concentrations ([Ca2+]o) up to 2.5 mM. At [Ca2+]o above 2.5 mM the differences in [Ca2+]i between the groups became less. The amplitude of the Ca2+ transients became higher in all groups with increasing [Ca2+]o (1, 2.5 and 5 mM), and was highest at all [Ca2+]o in hyperthyroid myocytes. The beta-agonist isoprenaline elevated peak [Ca2+]i during contraction and increased the rate of the decay of the Ca2+ transients to a greater extent in hypothyroid myocytes than in hyperthyroid myocytes. Depolarization with high [K+]o induced a large but transient [Ca2+]i overshoot in hypothyroid myocytes, but not in hyperthyroid myocytes, before a new elevated steady-state [Ca2+]i was reached, which was not different between the groups. When isoprenaline was added to K+ o-depolarized myocytes after a steady state was reached, a significantly larger extra increase in [Ca2+]i was measured in the hypothyroid group (28%) compared with the hyperthyroid group (8%). It is concluded that in cardiac tissue exposed to increasing amounts of thyroid hormones (1) [Ca2+]i increases at rest and during contraction in cardiomyocytes and (2) interventions which favour Ca2+ entry into the cytosol [( Ca2+]o elevation, high [K+]o, beta-agonists) tend to have less impact on Ca2+ homoeostasis.

A micro-perfusion chamber for single-cell fluorescence measurements

A versatile closed micro-perfusion chamber designed for single-cell fluorescence measurements under maximum microscopic magnification is described. Glass coverslips with adherent cells can be attached to the top or bottom of the chamber, depending on whether an inverted or an upright microscope is used. Eight conical holes drilled in the side of the chamber serve for the insertion of plugs with attachments for perfusion, rapid injection of small amounts of reagents, temperature measurements or for heating the interior of the chamber. Materials used in the construction of the chamber are non-toxic and resistant to standard sterilization procedures. Perfusion and temperature properties of the chamber are described. Single cell fluorescence measurements are presented in human monocyte-derived macrophages in which NAD(P)H and intracellular calcium are measured.

The membrane potential of the cellular slime mold Dictyostelium discoideum is mainly generated by an electrogenic proton pump

Trans membrane potential or ionic current changes may play a role in signal transduction and differentiation in the cellular slime mold dictyostelium discoideum. Therefore, the contribution of electrogenic ion pumps to the membrane potential of D. discoideum cells was investigated. the (negative) peak-value of the rapid potential transient, seen upon microelectrode impalement, was used to detect membrane potential changes upon changes in the external pH in the range of 5.5 to 8.0. The membrane potential was close to the Nernstian potential for protons over the pH range 5.5 to 7.5. The acid-induced changes in membrane potential were consistent with outward-proton pumping. The maximal membrane potential was at pH 7.5. Furthermore, the proton pump inhibitors diethylstilbestrol, miconazole and zearalenone directly depolarize the membrane. Cyanide and temperature decrease cause membrane depolarization as well. During recovery from cyanide poisoning a H+ efflux is present. From these measurements we conclude that the membrane potential of d. discoideum cells is mainly generated by an electrogenic proton pump. Measurements in cells with different extracellular potassium and H+ concentrations suggest a role for potassium in the function of the electrogenic proton pump. These results provide a framework for future research towards a possible role for the proton pump in signal transduction and differentiation.

Versatile perfusion chamber for high-magnification microscopy

The large number of culture or perfusion chambers reflects the necessity of researchers to develop them from time to time because of specific biologic or optical requirements. The paper described a new versatile perfusion chamber, which can be machined at low cost and with a very rapid assembly procedure. An additional interesting feature is the lock system with an annular threaded screw that fits the angle of the objective, thus increasing the field of observation.

Voltage-activated ionic channels and conductances in embryonic chick osteoblast cultures

Patch-clamp measurements were made on osteoblast-like cells isolated from embryonic chick calvaria. Cell-attached-patch measurements revealed two types of high conductance (100-250 pS) channels, which rapidly activated upon 50-100 mV depolarization. One type showed sustained and the other transient activation over a 10-sec period of depolarization. The single-channel conductances of these channel types were about 100 or 250 pS, depending on whether the pipettes were filled with a low K+ (3 mM) or high K+ (143 mM) saline, respectively. The different reversal potentials under these conditions were consistent with at least K+ conduction. Whole-cell measurements revealed the existence of two types of outward rectifying conductances. The first type conducts K+ ions and activates within 20-200 msec (depending on the stimulus) upon depolarizing voltage steps from less than -60 mV to greater than -30 mV. It inactivates almost completely with a time constant of 2-3 sec. Recovery from inactivation is biphasic with an initial rapid phase (1-2 sec) followed by a slow phase (greater than 20 sec). The second whole-cell conductance activates at positive membrane potentials of greater than +50 mV. It also rapidly turns on upon depolarizing voltage steps. Activation may partly disappear at the higher voltages. Its single channels of 140 pS conductance were identified in the whole cell and did conduct K+ ions but were not highly Cl- or Na+ selective. The results show that osteoblasts may express various types of voltage controlled ionic channels. We predict a role for such channels in mineral metabolism of bone tissue and its control by osteoblasts.

Electrophysiological properties of Dictyostelium derived from membrane potential measurements with microelectrodes

Electrical membrane properties of the cellular slime mold Dictyostelium discoideum were investigated with the use of intracellular microelectrodes. The rapid potential transients (1 msec) upon microelectrode penetration of normal cells had a negative-going peak-shaped time course. This indicates that penetration of a cell with a microelectrode causes a rapid depolarization, which can just be recorded by the microelectrode itself. Therefore, the initial (negative) peak potential transient value Ep (-19mV) should be used as an indicator of the resting membrane potential Em of D. discoideum before impalement, rather than the subsequent semistationary depolarized value En (-5 mV). Using enlarged cells such as giant mutant cells (Ep = -39 mV) and electrofused normal cells (Ep = -30 mV) improved the reliability of Ep as an indicator of Em. From the data we concluded that Em of D. discoideum cells bathed in (mM) 40 NaCl, 5 KCl and 1 CaCl2 is at least -50 mV. This potential was shown to be dependent on extracellular potassium. The average input resistance Ri of the impaled cells was 56 M omega for normal D. discoideum. However, our analysis indicates that the membrane resistance of these cells before impalement is greater than 1 G omega. Specific membrane capacitance was 1-3 pF/cm2. Long-term recording of the membrane potential showed the existence of a transient hyperpolarization following the rapid impalement transient. This hyperpolarization was associated with an increase in Ri of the impaled cell. It was followed by a depolarization, which was associated with a decrease in Ri. The depolarization time was dependent on the filling of the microelectrode. The present characterization of the electrical membrane properties of Dictyostelium cells is a first step in a membrane electrophysiological analysis of signal transduction in cellular slime molds.

Extracellular ATP induces a large nonselective conductance in macrophage plasma membranes

Extracellular ATP in its tetra-anionic form (ATP4-) induces ion fluxes and membrane depolarization in the mouse macrophage-like cell line J774.2 and in resident mouse macrophages. We analyzed the effects of extracellular ATP4- by both patch-clamp and intracellular microelectrode techniques. Whole-cell patch-configuration membrane potential measurements on J774.2 cells revealed that ATP4- -induced depolarization occurred within 40 ms of pulsed application of ATP and was completely reversible. The depolarizations were accompanied by a dramatic increase in membrane conductance and showed no sign of adaptation to ATP over a period of 30 min. At 5 mM total ATP (ATPt) the whole-cell conductance was approximately 10 nS, and an upper limit of 20 pS for a single-channel conductance has been established. The reversal potential associated with the ATP-induced depolarization at asymmetric K+, Na+, Ca2+, and Cl- concentrations across the membrane was 0 mV. In patch-clamped cells depolarization was complete at 20 microM ATP4-, and repolarization from full depolarization occurred in approximately 5 s. In contrast, in intact cells measured by microelectrode impalement, complete depolarization occurred at approximately 2 mM ATP4- and repolarization was much slower (approximately 100 min). These findings indicate that the changes in intracellular ionic composition that occur after ATP treatment affect the rate of cell repolarization. At lower concentrations of ATP, potassium conductances modulated the depolarizing effect of ATP. ATP also depolarized mouse peritoneal macrophages, but a variant cell line (ATPR B2), derived from J774.2 cells by prolonged exposure to ATP, was insensitive to ATP. Our results provide a membrane electrophysiological description and analysis of a large nonselective plasma membrane conductance of macrophages induced by extracellular ATP.

Phagocytosis by human macrophages is accompanied by changes in ionic channel currents

The present study has shown that changes in ionic channel currents accompany the phagocytosis of particles by mononuclear phagocytes. The patch-clamp technique in the cell-attached configuration was applied to human monocyte-derived macrophages to measure the activity of single transmembrane ionic channels in intact cells. During such measurements, IgG-opsonized and non-opsonized latex particles were offered for phagocytosis under continuous video-microscopical observation. Single particles were presented to the phagocytes at a membrane location some distance from that of the patch electrode. After a lag period following particle attachment, enhanced inward and outward time-variant single channel currents coinciding with particle engulfment were observed. On the basis of current-voltage characteristics and membrane potential measurements, the outward-directed channels were identified as K+ channels. Phagocytosis was also accompanied by slow transient changes in background membrane currents, probably due to changes in the membrane potential of the phagocytosing cell. Phagocytosis of IgG-coated latex particles differed from phagocytosis of uncoated or albumin-coated particles by a shorter lag time between particle attachment and the onset of enhanced ionic channel activity.

Intracellular K+, Na+ and Cl- concentrations and membrane potential in human monocytes

The relationship between the resting membrane potential and the intracellular ionic concentrations in human monocytes was investigated. Cell volume, cell water content, and amount of intracellular K+, Na+, and Cl- were measured to determine the intracellular concentrations of K+ (Ki), Na+ (Nai) and Cl- (Cli) of monocytes, and of lymphocytes and neutrophils. Values found for monocytes were similar to those for neutrophils, i.e., cell volumes were 346 and 345 micron3, respectively, cell water content 78%, and Ki, 128 and 125, Nai, 24 and 26, and Cli, 102 and 103 mmol/l cell water, respectively. Lymphocytes, however, had different values: 181 micron3 cell volume, 77% cell water content, and for Ki, Nai, and Cli, 165, 37, and 91 mmol/l cell water, respectively. The resting membrane potential of cultured human monocytes (range -30 to -40 mV), determined by measurement of the peak potential occurring within the first milliseconds after microelectrode entry, was most dependent on extracellular K+, followed by Cl-, and Na+. The membrane permeability ratio of Cl- to K+ was estimated by use of the constant field equation to be 0.23 (range 0.22 to 0.30).

Ionic channels and membrane hyperpolarization in human macrophages

Microelectrode impalement of human macrophages evokes a transient hyperpolarizing response (HR) of the membrane potential. This HR was found to be dependent on the extracellular concentration of K+ but not on that of Na+ or Cl-. It was not influenced by low temperature (12 degrees C) or by 0.2 mM ouabain, but was blocked by 0.2 mM quinine or 0.2 mM Mg2+-EGTA. These findings indicate that the HR in human macrophages is caused by the activation of a K+ (Ca2+) conductance. Two types of ionic channels were identified in intact cells by use of the patch-clamp technique in the cell-attached-patch configuration, low and high-conductance voltage-dependent K+ channels. The low-conductance channels had a mean conductance of 38 pS with Na+-saline and 32 pS with K+-saline in the pipette. The high-conductance channels had a conductance of 101 and 114 pS with Na+- and K+-saline in the pipette, respectively. Cell-attached patch measurements made during evocation of an HR by microelectrode penetration showed enhanced channel activity associated with the development of the HR. These channels were also high-conductance channels (171 pS with Na+- and 165 pS K+-saline in the pipette) and were voltage dependent. They were, however, active at less positive potentials than the high-conductance K+ channels seen prior to the microelectrode-evoked HR. It is concluded that the high-conductance voltage-dependent ionic channels active during the HR in human macrophages contribute to the development of the HR.

Hairy cell leukemia: in-vitro proliferation and pseudo-colony formation

In an established double layer clonogenic assay, the PHA-leukocyte feeder colony assay, hairy cell leukemia (HCL) cells formed strong aggregates simulating colonies. After irradiation with 50 Gy, colony formation persisted. Even in a modified colony assay consisting of agar 0.5% overlayered by methylcellulose 0.9%, cell aggregation was still possible due to increasing fluidity of the methylcellulose during the culture period. Time-lapse video recordings confirmed prominent cell motility leading to pseudo-colony formation. Studies with bromodeoxyuridine incorporation showed a low proliferation index (up to 13%) of hairy cells. In conclusion, any assay that facilitates cell motility is unsuitable to study HCL colony growth.

Intracellular microelectrode measurements in small cells evaluated with the patch clamp technique

Microelectrode penetration of small cells leads to a sustained depolarization of the resting membrane potential due to a transmembrane shunt resistance (Rs) introduced by the microelectrode. This has led to underestimation of the resting membrane potential of various cell types. However, measurement of the fast potential transient occurring within the first few milliseconds after microelectrode penetration can provide information about pre-impalement membrane electrophysiological properties. We have analyzed an equivalent circuit of a microelectrode measurement to establish the conditions under which the peak of the impalement transients (Ep) approaches the pre-impalement resting membrane potential (Em) of small cells most closely. The simulation studies showed that this is the case when the capacitance of the microelectrode is low and the membrane capacitance of the cell high. In experiments performed to assess the reliability of Ep as a measure of Em, whole-cell patch clamp measurements were performed in the current clamp mode to monitor, free from the effects of Rs, Em in cultured human monocytes. Microelectrode impalement of such patch clamped cells and measurement of Ep made it possible to detect correlation between Ep and Em and showed that for small cells such as human monocytes Ep is on average 6 mV less negative than the resting membrane potential.