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PubMed1990

Multiple site optical recording of transmembrane voltage (MSORTV), single-unit recordings, and evoked field potentials from the olfactory bulb of skate (Raja erinacea).

1. Multiple site optical recording of transmembrane voltage (MSORTV), together with conventional extracellular electrophysiological techniques were utilized with in vivo and in vitro preparations of the olfactory bulb of the Atlantic skate Raja erinacea to analyze electrical activity simultaneously in layers deep to the glomerular layer. 2. In the living animals and the in vitro isolated olfactory bulb, orthodromic stimulation evoked a compound action potential in the olfactory nerve fibers, followed by a series of early field-potential waves (N1, P1, N2, P2, N3, and N4). During paired stimulation experiments, unusual patterns of facilitation and suppression were observed for the N2 wave. 3. After orthodromic stimulation, single units, presumably mitral/tufted cells, exhibited a period of early discharge, followed by a period of suppression of spontaneous activity and of their test response in a pair stimulation paradigm. Some neurons also exhibited a labile period of reexcitation that was accompanied by a late surface negative field potential; these responses were also present in olfactory bulb slices. 4. Extrinsic absorption changes obtained from 500-microns saggital slices of the olfactory bulb, stained with the pyrazooxonal dye RH-155, consisted mainly of two types of depolarizing responses, a fast and a slow component, followed under some conditions by a late hyperpolarization. All signals exhibited wavelength dependences typical of the action spectrum of RH-155 and were abolished in the presence of tetrodotoxin (TTX) or high K+ in the bath. 5. The fast component of the optical signal represents synchronous compound action potentials conducted by the olfactory nerve fibers or evoked in the mitral/tufted somata and axonal pathways. The slow depolarizing optical signal appeared, after orthodromic stimuli, mainly in the zone between the glomeruli and the mitral/tufted layer; barium (1-10 mM), which depolarizes glial cells, increased its size and duration, suggesting that this signal does not reflect a glial response to [K+]o. 6. Different condition/test (C/T) intervals produced partial or complete suppression of the test response, depending on the recording site and the stimulus intensity. Just threshold orthodromic stimuli evoked an intermediate period of facilitation of the slow signals. A similar period was also observed in the N2 wave of the field potential. 7. Calcium channel blockers such as cadmium ion, or a low Ca2+ medium, suppressed the slow optical component whether evoked by orthodromic, antidromic, or direct stimulation. gamma-Aminobutyric acid (GABA) and baclofen also reduced or blocked the slow component of the extrinsic absorption signal.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Potassium secretion in the guinea pig distal colon.

Active K+ secretion in guinea pig distal colon was studied in vitro in Ussing chambers. Changes in short-circuit current (Isc), transepithelial conductance (Gt), and the unidirectional flux of 42K from serosa to mucosa (JKsm) were determined under a variety of physiological and pharmacological conditions. Mucosal tetraethylammonium (TEA) (10 or 30 mM) increased Isc, while it decreased Gt and JKsm. Seroal bumetanide (10(-4) M) also caused an increase in Isc and decreases in Gt and JKsm. The effects produced by TEA were abolished in the presence of bumetanide. The increase in Isc caused by bumetanide was greatly reduced by mucosal high-K+ conditions. Isoproterenol (10(-6) M), a beta-adrenergic agonist, elicited a decrease in Isc and an increase in Gt. Responses to isoproterenol (10(-6) M) were reduced or abolished by mucosal TEA, serosal bumetanide, serosal ouabain (10(-4) M), and serosal Na+- or Cl(-)-free conditions. Mucosal high K+ also reduced the isoproterenol-induced decrease in Isc. These results suggest that K+ secretion is electrogenic and dependent on the bumetanide-sensitive cotransport in the basolateral membrane. K+ exit across the apical membrane might be conductive and sensitive to TEA. In addition, beta-adrenergic agonists might stimulate K+ secretion.

Animals↗
PubMed1975

A study of the anticholinergic and antispasmodic activity of oxybutynin (Ditropan) on rabbit detrusor.

Experiments have been conducted which show that while the tertiary amine oxybutynin has only moderate in vitro anticholinergic and antihistaminic activity, it is a potent inhibitor of barium chloride-induced spasms of rabbit detrusor muscle. Oxybutynin exerts 1/13 the anticholinergic activity of propantheline and 1/4 that of atropine, but produces approximately 2x the inhibition of barium chloride-induced spasm than propantheline and 10x the inhibition produced by atropine. In sum, oxybutynin possesses a notable antispasmodic activity distinct from its anticholinergic activity and stronger than that of atropine, propantheline, or methantheline, which may prove useful in the treatment of smooth muscle hypermotility.

Animals↗
PubMed1988

Whole-cell recordings of ionic currents in bovine somatotrophs and their involvement in growth hormone secretion.

1. The whole-cell mode of the patch-clamp technique was used to record voltage-activated cationic currents in immunocytochemically identified bovine somatotrophs. 2. In current-clamp mode, cells had a resting membrane potential of -83.0 +/- 4.5 mV, and an input resistance of 8.4 +/- 2.1 G omega. Cells rarely fired action potentials spontaneously, but fired one to three action potentials in response to a suprathreshold current pulse. 3. Under voltage clamp, in Ca2+-free media, the action potential was shown to be composed of a TTX-sensitive inward Na+ current and an outward K+ current. 4. The isolated Na+ current had a threshold of approximately -50 mV, and rapidly activated and then inactivated to a small steady-state current. Peak Na+ current amplitude with 140 mM-external Na+ was 341.1 +/- 33.5 pA (n = 14) at a membrane potential of -32.1 +/- 2.4 mV (n = 14). 5. With Ca2+ or Ba2+ (5-30 mM) as the only membrane-permeable cation, voltage pulses to potentials more positive than -55 mV from a holding potential of -80 mV revealed a rapidly activating current component that was followed by a second, very slowly inactivating, current component, most clearly seen with Ba2+. Both components were maximally activated between 0 and +10 mV, were TTX insensitive, but were blocked by 4 mM-Co2+. 6. Three components of the isolated K+ current were identified (IA, IK and IK(Ca] by their voltage sensitivity, Ca2+ dependence and their response to 4-aminopyridine (4-AP) and tetraethylammonium (TEA). 7. Growth hormone (GH)-releasing hormone (GHRH) applied to cells under whole-cell voltage clamp had no effect on either steady-state or voltage-activated ionic currents. This is probably due to dialysis of cytoplasmic compounds vital for GHRH activation of the cell. 8. Both basal and GHRH-stimulated GH secretion were unaffected by TTX, implying that the Na+ action potential is not critical for such release. In contrast the Ca2+ channel blocker Co2+ attenuated GH release in both cases. The K+ channel blocker TEA stimulated GH release above basal and GHRH-stimulated levels.

Action Potentials↗
PubMed2006

Syntheses and structures of strontium, barium, and europium bis(diphosphanylamido) complexes.

Bis(diphosphanylamido) complexes of strontium and europium, [{(Ph(2)P)(2)N}(2)M(THF)(3)] (M = Sr (1), Eu (2)), have been prepared by reaction of [K(THF)(n)()][N(PPh(2))(2)] (n = 1.25, 1.5) and MI(2). The single-crystal X-ray structures of compounds 1 and 2 always show a eta(2) coordination of the ligand via the nitrogen and one phosphorus atom. In solution, a dynamic behavior of the ligand is observed, which is caused by the rapid exchange of the two different phosphorus atoms. As a result of the radius of the larger ion, treatment of [K(THF)(n)()][N(PPh(2))(2)] with BaI(2) gives the coordination polymer [{(Ph(2)P)(2)N}(2)Ba(THF){(Ph(2)P)(2)N}K](n)() (3). Two of the three {(Ph(2)P)(2)N}(-) ligands of compound 3 bind to the metal in eta(2) (N, P) while the third shows a heteroallylic (P, P) coordination mode. In the solid state, the infinite chain is formally held together by pi coordination of the phenyl rings to the potassium atoms.

Journal Article↗
PubMed2006

Modulated structure of potassium sodium strontium barium niobates (KNSBN): harmonic solution.

The structures of two specimens of the (K(1 - y)Na(y))(2F - 2)(Sr(x)Ba(1 - x))(2 - F)Nb2O6 family (KNSBN) have been solved and refined (x(I) = 0.6, y(I) = 0.45, F(I) = 1.07 and x(II) = 0.72, y(II) = 0.45, F(II) = 1.08). The KNSBN compounds appear to be incommensurately modulated, as described in a five-dimensional superspace approach with the tetragonal P4bm (pp1/2, p - p1/2) superspace group. Their modulation wavevectors are almost independent of the composition. The description of the modulation is restricted to first-order harmonics in order to limit the number of refined parameters. The modulation mainly affects the positions of the O atoms and their displacements depend on the Sr/Ba ratio. The structural models for the two compounds are not only almost identical, but also analogous to the structural model of the Sr(x)Ba(1 - x)Nb2O6 parent compound: doping with K+ and Na+ cations has no significant influence on the incommensurate modulation, contrary to the strong dependence observed for the physical properties.

Journal Article↗
PubMed2006

Role of donor and secondary interactions in the structures and thermal properties of alkaline-earth and rare-earth metal pyrazolates.

The addition of neutral coligands to reduce the aggregation and improve the volatility of potential heavy alkaline-earth metal chemical vapor deposition (CVD) precursors has typically resulted in liberation of the coligand upon heating. A new series of dinuclear alkaline-earth and rare-earth metal pyrazolates, bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)calcium] (1), bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)strontium] (2), and bis[bis(3,5-di-tert-butylpyrazolato)bis(tetrahydrofuran)barium] (3), have been obtained from our previous donor-free oligonuclear complexes [{M(3,5-tBu2pz)2}n] (5, M = Ca, n = 3; 6, M = Sr, n = 4; 7, M = Ba, n = 6) by treatment with tetrahydrofuran (THF). Compounds 1-3, as well as the europium analogue bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)europium(II)] (4), can also be prepared by direct reaction of the metals and pyrazole in THF and anhydrous liquid ammonia. Recrystallization from hexane led to single crystals of 2-4, while the powder diffraction pattern of 1 revealed it to be isostructural with the previously published bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)ytterbium(II)] (8), providing important insight into differences and similarities between the two groups of metals. Detailed structural analysis of the compounds reveals secondary interactions including pi-bonding and agostic interactions, which are considered essential in stabilizing the metal complexes. The direct comparison of structural features and thermal properties (as evaluated by thermogravimetric analysis and sublimation studies) of the donor-free oligonuclear and the donor-containing dinuclear species offers a better understanding of the role of donors and secondary interactions.

Journal Article↗
PubMed1999

Involvement of calcium inhibitable binding to the cell wall in the fungicidal activity of CAN-296.

CAN-296 is a heat stable, complex carbohydrate (molecular mass 4300 Da) isolated from the cell wall of the filamentous fungus Mucor rouxii. It possesses potent in-vitro fungicidal activity against a wide spectrum of pathogenic yeasts, including azole-resistant isolates of Candida albicans and Candida glabrata. As a preliminary step in the study of the mode of action of this novel antifungal agent, we investigated the effect of various cations on the antifungal activity as well as the binding of CAN-296 to intact cells and cell-wall fractions of C. albicans. The antifungal activity of CAN-296 was inhibited by low concentrations of calcium, magnesium and lithium and by high concentrations of barium, cobalt and manganese, but not by potassium and copper. The calcium-mediated inhibition of the antifungal activity of CAN-296 was readily reversible by the removal of calcium by dialysis, and the fungicidal activity of the inhibited compound was fully restored. The uptake/binding of CAN-296 to intact cells and to the cell-wall fraction of C. albicans was time and concentration dependent. Maximum uptake/binding was obtained at 5 mg/L within 60 min and was associated with the aggregation of intact cells. Washing intact cells and the cell-wall fraction preincubated with radiolabelled CAN-296 with 150-fold excess of unlabelled compound failed to remove CAN-296 associated with the intact cells and the cell-wall fraction, suggesting that the binding of CAN-296 to C. albicans is tight. The uptake/binding of CAN-296 and the drug-mediated aggregation of intact cells were inhibited by calcium in a concentration-dependent manner. The fact that CAN-296 is a fungicidal agent that binds to intact cells and the cell-wall fraction of C. albicans very tightly, together with the observation that calcium was able to inhibit the fungicidal activity as well as the uptake/binding of CAN-296, suggests that the mode of action of this novel antifungal agent may involve interaction with the cell wall of C. albicans.

Antifungal Agents↗
PubMed1975

[Spasmolytic activity of a piperazine derivative under the code number of 4P-79].

The author examined the pharmacologic spasmolytic action of a pyperasine derivative under the code 4P-79. She examined the effect of the compound on four types of spasms, induced by acethylcholine, nicotine, histamine and serotonine on an isolated rabbit intestine. The mean effective concentrations were determined and they were compared with the mean effective concentrations of papaverine and benzylharmine, estimated in parallel experiments. It was found that 4P-79 had high spasmolytic activity, surpassing several times that of the preparations used for comparison. There was a marked antiserotonine effect on the first place. The compound was examined also on an intestine "in situ" by the method of Nikolaev Comparative experiments with papaverine and deseryl were conducted.

Acetylcholine↗
PubMed1980

[Effects of adenosine compounds on the contractile response of isolated canine blood vessels to various agonists (author's transl)].

Effects of adenine and adenosine compounds (adenosine, AMP, ATP, cyclic AMP and dibutyryl cyclic AMP) on the contractile responses of helically cut strips of canine superior mesenteric arteries to various agonists (K+, norepinephrine, angiotensin II and Ba2+), to transmural electrical stimulation and on Ca2+ contractures of K+-depolarized strips were studied. The contractions induced by these agonists were suppressed, dose dependently, but to a different degree by these adenosine compounds, with the exception of the potentiating action of ATP on the Ba2+-induced contraction. The suppression of the effect of norepinephrine, angiotensin II and transmural stimulation was appreciably greater than that of K+ and Ba2+. Adenine was equally or more effective in inhibiting the contractions induced by these agonists than were the other adenosine compounds used. The order of relative inhibitory potency was adenine Greater Than or Equal to adenosine Greater Than or Equal to AMP = ATP Greater Than cyclic AMP = dibutyryl cyclic AMP. The ATP-induced contraction was influenced in a different manner by each adenosine compound. Adenosine and cyclic AMP did not affect the ATP-induced contraction but AMP and dibutyryl cyclic AMP in a narrow range of concentrations enhanced the contraction. On the contrary, adenine and ATP inhibited the ATP contraction, dose-dependently, resulting in tachyphylaxis, with the repeated application of ATP. The present results suggest that adenine moiety in the molecule plays an important role in the inhibitory action of adenosine compounds, and that the antagonistic action of adenosine compounds is due to their inhibitory actions on Ca2+-influx and Ca2+-release from cell stores.

Adenine Nucleotides↗
PubMed1993

[The radionuclide diagnosis of post-gastric resection disorders].

The article studies the possibilities of radionuclide method in disclosing the basic postgastroresectional syndromes: dumping syndrome, duodenogastric reflux and afferent loop syndrome. After resection of stomach 92 patients were examined throughout a period from 1 to 10 years. During dynamic scintigraphy of liver characteristic changes were disclosed in biliary secretory system which could have diagnostic significance. This method gives the possibility to determine the frequency, duration and volume of duodenogastric reflux. It was found out that Roux's [correction of Rue's] method of resection have resulted in minimal number of duodenogastric refluxes. Dynamic scintigraphy of stomach is useful for studying evacuative function of the resected stomach and for afferent loop syndrome diagnosis, which sometimes is more informative than a wide-spread barium sulfate roentgenological method.

Diagnosis, Differential↗
PubMed1985

Ionic channels in epithelial cell membranes.

This review focused on results obtained with methods that allow studies of ionic channels in situ, namely, patch clamping and current-noise analysis. We reported findings for ionic channels in apical and basolateral plasma membranes of various tight and leaky epithelia from a wide range of animal species and tissues. As for ionic channel "species," we restricted ourselves to the discussion of cation-specific (Na+ or K+), hybrid (Na+ and K+), and Cl- channels. For the K+-specific channels it can be said that their properties in conduction (multisite, single file), selectivity (only "K+-like" cations), and blocking behavior (Ba2+, Cs+, TEA) much resemble those observed for K+ channels in excitable membranes. This seems to include also the Ca2+-activated "maxi" K+ channel. Thus, K+ channels in excitable membranes and K+ channels in epithelia appear to be very closely related in their basic structural principles. This is, however, not at all unexpected, because K+ channels provide the dominant permeability characteristics of nearly all plasma membranes from symmetrical and epithelial cells. An exception is, of course, apical membranes of tight epithelia whose duty is Na+ absorption against large electrochemical gradients in a usually anisosmotic environment. Here, Na+ channels dominate, although a minor fraction of membrane permeability comes from K+ channels, as in frog skin, colon, or distal nephron. Epithelial Na+ channels are different from excitable Na+ channels in that they 1) are far more selective and 2) seem to be chemically rather than electrically gated. Furthermore, their specific blockers belong to very different chemical families, although a guanidinium/amidinium moiety is a common feature (TTX vs. amiloride). [For a more detailed summary of Na+ channel properties see sect. IV H.] Most interesting is the occurrence of relatively nonselective cationic (hybrid) channels in apical membranes of tight epithelia, like larval or adult frog skin. Here, not only the weak selectivity is astonishing but also the fact that these channels react with so-called K+-channel-specific (Ba2+, TEA) as well as with Na+-channel-specific (amiloride, BIG) compounds. Moreover, this cross-reactivity does not seem to be inhibitory but, on the contrary, stimulating. Clearly these channels may become a fascinating object with which to assess whether Na+ and K+ channels are not only structurally but also genetically related and whether they can somehow be converted into each other.(ABSTRACT TRUNCATED AT 400 WORDS)

Aldosterone↗
PubMed1993

ATP-inhibited and Ca(2+)-dependent K+ channels in the soma membrane of cultured leech Retzius neurons.

The properties of one ATP-inhibited and one Ca(2+)-dependent K+ channel were investigated by the patch-clamp technique in the soma membrane of leech Retzius neurons in primary culture. Both channels rectify at negative potentials. The ATP-inhibited K+ channel with a mean conductance of 112 pS is reversibly blocked by ATP (Ki = 100 microM), TEA (Ki = 0.8 mM) and 10 mM Ba2+ and irreversibly blocked by 10 nM glibenclamide and 10 microM tolbutamide. It is Ca2+ and voltage independent. Its open state probability (Po) decreases significantly when the pH at the cytoplasmic face of inside-out patches is altered from physiological to acid pH values. The Ca(2+)-dependent K+ channel with a mean conductance of 114 pS shows a bell-shaped Ca2+ dependence of Po with a maximum at pCa 7-8 at the cytoplasmic face of the membrane. The Po is voltage independent at the physiologically relevant V range. Ba2+ (10 MM) reduces the single channel amplitude by around 25% (ATP, TEA, glibenclamide, tolbutamide, and Ba2+ were applied to the cytoplasmic face of the membrane). We conclude that the ATP-dependent K+ channel may play a role in maintaining the membrane potential constant--independently from the energy state of the cell. The Ca(2+)-dependent K+ channel may play a role in generating the resting membrane potential of leech Retzius neurons as it shows maximum activity at the physiological intracellular Ca2+ concentration.

Adenosine Triphosphate↗
PubMed1988

Electrophysiological study of transport systems in isolated perfused pancreatic ducts: properties of the basolateral membrane.

In order to study the mechanism of pancreatic HCO3- transport, a perfused preparation of isolated intra- and interlobular ducts (i.d. 20-40 microns) of rat pancreas was developed. Responses of the epithelium to changes in the bath ionic concentration and to addition of transport inhibitors was monitored by electrophysiological techniques. In this report some properties of the basolateral membrane of pancreatic duct cells are described. The transepithelial potential difference (PDte) in ducts bathed in HCO3(-)-free and HCO3(-)-containing solution was -0.8 and -2.6 mV, respectively. The equivalent short circuit current (Isc) under similar conditions was 26 and 50 microA . cm-2. The specific transepithelial resistance (Rte) was 88 omega cm2. In control solutions the PD across the basolateral membrane (PDbl) was -63 +/- 1 mV (n = 314). Ouabain (3 mmol/l) depolarized PDbl by 4.8 +/- 1.1 mV (n = 6) within less than 10 s. When the bath K+ concentration was increased from 5 to 20 mmol/l, PDbl depolarized by 15.9 +/- 0.9 mV (n = 50). The same K+ concentration step had no effect on PDbl if the ducts were exposed to Ba2+, a K+ channel blocker. Application of Ba2+ (1 mmol/l) alone depolarized PDbl by 26.4 +/- 1.4 mV (n = 19), while another K+ channel blocker TEA+ (50 mmol/l) depolarized PDbl only by 7.7 +/- 2.0 mV (n = 9). Addition of amiloride (1 mmol/l) to the bath caused 3-4 mV depolarization of PDbl. Furosemide (0.1 mmol/l) and SITS (0.1 mmol/l) had no effect on PDbl. An increase in the bath HCO3- concentration from 0 to 25 mmol/l produced fast and sustained depolarization of PDbl by 8.5 +/- 1.0 mV (n = 149). It was investigated whether the effect of HCO3- was due to a Na+-dependent transport mechanism on the basolateral membrane, where the ion complex transferred into the cell would be positively charged, or whether it was due to decreased K+ conductance caused by lowered intracellular pH. Experiments showed that the HCO3- effect was present even when the bath Na+ concentration was reduced to a nominal value of 0 mmol/l. Similarly, the HCO3- effect remained unchanged after Ba2+ (5 mmol/l) was added to the bath. The results indicate that on the basolateral membrane of duct cells there is a ouabain sensitive (Na+ + K+)-ATPase, a Ba2+ sensitive K+ conductance and an amiloride sensitive Na+/H+ antiport. The HCO3- effect on PDbl is most likely due to rheogenic anion exit across the luminal membrane.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1986

Influence of external barium and potassium on potassium efflux in depolarized frog sartorius muscles.

Efflux of 42K+ was measured in frog sartorius muscles equilibrated in depolarizing solutions with external K+ concentrations [( K+]0) between 75 and 300 mM and NaCl concentrations of 60, 120, or 240 mM. For several combinations of KCl and NaCl, steady-state internal potentials (Vi) were the same for different [K+]0. For the range of Vi examined, K+ efflux occurs principally through the K+ inward rectifier channels. When external K+ is removed Vi remains constant for 2 to 3 hr because of the high membrane conductance to Cl-, but K+ efflux drops by about one order of magnitude. External Ba2+ in the presence or absence of external K+ produces an inhibition of K+ efflux described by a relation of the form u = (u1/(1 + C [Ba2+]0] + u2, where u is the uninhibited fraction of K+ efflux; u1, u2 and C are constants; and u1 + u2 = 1. C depends both on [K+]0 and Vi. When [K+]0 greater than or equal to 75 mM, increasing [K+]0 at constant Vi reduces Ba2+ sensitivity. For constant Vi greater than or equal to -30 mV, Ba2+ sensitivity is less when [K+]0 = 0 than when [K+]0 greater than or equal to 75 mM. When [K+]0 = 0, Ba2+ sensitivity decreases as Vi is made more positive. The dependence of the Ba2+ sensitivity on Vi at constant [K+]0 is greater when [K+]0 = 0 than when [K+]0 greater than or equal to 75 mM. Both the activation of K+ efflux by external K+ and the Ba2+ inhibition of K+ efflux can be explained on the basis of two membrane control sites associated with each channel. When both sites are occupied by K+, the channels are in a high flux state. When one or both sites are empty, the channels are in a low, nonzero flux state. When Ba2+ occupies either site, K+ efflux is further reduced. The reduction of Ba2+-sensitivity by increasing [K+]0 at high [K+]0 is attributable to the displacement of Ba2+ from the control sites by K+. The increased Ba2+ sensitivity produced by going from [K+]0 = 0 to [K+] greater than or equal to 75 mM when Vi greater than or equal to -30 mV is attributable to states in which Ba2+ occupies one site and K+ the other when [K+]0 not equal to 0.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Patch-clamp studies in human macrophages: single-channel and whole-cell characterization of two K+ conductances.

Human peripheral blood monocytes cultured for varying periods of time were studied using whole-cell and single-channel patch-clamp recording techniques. Whole-cell recordings revealed both an outward K current activating at potentials greater than 20 mV and an inwardly rectifying K current present at potentials negative to -60 mV. Tail currents elicited by voltage steps that activated outward current reversed near EK, indicating that the outward current was due to a K conductance. The I-V curve for the macroscopic outward current was similar to the mean single-channel I-V curve for the large conductance (240 pS in symmetrical K) calcium-activated K channel present in these cells. TEA and charybdotoxin blocked the whole-cell outward current and the single-channel current. Excised and cell-attached single-channel data showed that calcium-activated K channels were absent in freshly isolated monocytes but were present in greater than 85% of patches from macrophages cultured for greater than 7 days. Only 35% of the human macrophages cultured for greater than 7 days exhibited whole-cell inward currents. The inward current was blocked by external barium and increased when [K]o increased. Inward-rectifying single-channel currents with a conductance of 28 pS were present in cells exhibiting inward whole-cell currents. These single-channel currents are similar to those described in detail in J774.1 cells (L.C. McKinney & E.K. Gallin, J. Membrane Biol. 103:41-53, 1988).

Barium↗