Electrophysiology of phagocytic membranes: intracellular K+ activity and K+ equilibrium potential in macrophage polykaryons

The intracellular K activity (aKi) and membrane potential of sensory neurons in the leech central nervous system were measured in normal and altered external K+ concentrations, [K+]o, using double-barreled, liquid ion-exchanger microelectrodes. In control experiments membrane potential measurements were made using potassium chloride-filled single-barreled microelectrodes. All values are means +/- SD. At the normal [K+]o (4 mM) the mean aKi of all cells tested was 72.6 +/- 10.6 mM (n = 40) and the average membrane potential was -47.3 +/- 5.2 mM (n = 40). When measured with single-barreled microelectrodes, the membrane potential averaged -45.3 +/- 2.9 mV (n = 12). Assuming an intracellular K+ activity coefficient of 0.75, the intracellular K+ concentration of sensory neurons would be 96.8 +/- 14.1 mM). With an extracellular K+ concentration of 5.8 mM in the intact ganglion compared to the K+ concentration of 4 mM in the bath, the K+ equilibrium potential was -71.5 mV. When the ganglion capsule was opened, the extracellular K+ concentrations in the ganglion were similar to that of the bathing medium and the calculated K+ equilibrium potential was -81 mV. The membrane of sensory neurons depolarized following the changes to elevated [K+]o (greater than or equal to 10-100 mM), whereas aKi changed only little or not at all. At very low [K+]o (0.2, 0 mM) aKi and membrane potential showed little short-term (less than 3 min) effect but began to change after longer exposure (greater than 3 min). Reduction of [K+]o from 4 to 0.2 mM (or 0 mM) produced first a slow, and then a more rapid decrease of aKi and membrane resistance, accompanied by a slow membrane hyperpolarization. Following readdition of normal [K+]o, the membrane first depolarized and then transiently hyperpolarized, eventually returning slowly to the normal membrane potential.(ABSTRACT TRUNCATED AT 400 WORDS)

Download Full-text

The effect of extracellular potassium on the intracellular potassium ion activity and transmembrane potentials of beating canine cardiac Purkinje fibers.

The Journal of General Physiology ◽

10.1085/jgp.69.4.463 ◽

1977 ◽

Vol 69 (4) ◽

pp. 463-474 ◽

Cited By ~ 28

Author(s):

D S Miura ◽

B F Hoffman ◽

M R Rosen

Keyword(s):

Equilibrium Potential ◽

Extracellular Potassium ◽

Purkinje Fibers ◽

Transmembrane Potentials ◽

Cardiac Purkinje Fibers ◽

K Concentration ◽

Range Of Values ◽

Intracellular K Activity ◽

Liquid Ion Exchanger ◽

K Activity

We used open tip microelectrodes containing a K+-sensitive liquid ion exchanger to determine directly the intracellular K+ activity in beating canine cardiac Purkinje fibers. For preparations superfused with Tyrode's solution in which the K+ concentration was 4.0 mM, intracellular K+ activity (ak) was 130.0+/-2.3 mM (mean+/-SE) at 37 degrees C. The calculated K+ equilibrium potential (EK) was -100.6+/-0.5 mV. Maximum diastolic potential (ED) and resting transmembrane potential (EM) were measured with conventional microelectrodes filled with 3 M KCl and were -90.6+/-0.3 and -84.4+/-0.4 mV, respectively. When [K+]o was decreased to 2.0 mM or increased to 6.0, 10.0, and 16.0 mM, ak remained the same. At [K+]o=2.0, ED was -97.3+/-0.4 and Em -86.0+/-0.7 mV; at [K+]o=16.0, ED fell to -53.8+/-0.4 mV and Em to the same value. Over this range of values for [K+]o, EK changed from -119.0+/-0.3 to -63.6+/-0.2 mV. These values for EK are consistent with those previously estimated indirectly by other techniques.

Download Full-text

Measurements of the Intracellular Potassium Activity of Retzius Cells in the Leech Central Nervous System

Journal of Experimental Biology ◽

10.1242/jeb.91.1.87 ◽

1981 ◽

Vol 91 (1) ◽

pp. 87-101

Author(s):

JOACHIM W. DEITMER ◽

WOLF R. SCHLUE

Keyword(s):

Cell Membrane ◽

External Solution ◽

Equilibrium Potential ◽

The Mean ◽

K Concentration ◽

Retzius Cells ◽

Intracellular K Activity ◽

K Permeability ◽

K Activity ◽

External K

The intracellular K activity of leech Retzius cells was measured using double-barrelled, liquid ion exchanger, microelectrodes. At the normal external K+ concentration of 4 mm (equivalent to 3 mm-K activity, assuming an activity coefficient of 0.75) the mean K activity was 101.3 ± 7.6 mm (S.D., n = 14) in the cell bodies, and 4.35 ± 0.4 mV (n = 27) in the extracellular spaces surrounding them, indicating a K+ equilibrium potential of - 80 mV. The mean membrane potential was - 43.6 + 4.9 mV (n = 14). In a K-free external solution, or in the presence of 5 × 10−4m-ouabain, the intracellular K activity decreased by up to 14 mm min−1. This indicates an efflux of K+ ions across the cell membrane of approximately 2 × 10−10 mol cm−2s, and an apparent K+ permeability coefficient of 8 × 10−8 cms−1. The cell membrane depolarized upon removal of K+ and upon addition of ouabain, and transiently hyperpolarized beyond its initial level on return to the normal external K+ concentration. The recovery from this hyperpolarization paralleled the increase of the intracellular K activity following the re-addition of K+. Our results suggest that, despite the high K+ permeability of the Retzius cell membrane, the intracellular K activity is maintained at a high level by an electrogenic pump.

Download Full-text

Intracellular K+ activity and its relation to basolateral membrane ion transport in Necturus gallbladder epithelium.

The Journal of General Physiology ◽

10.1085/jgp.76.1.33 ◽

1980 ◽

Vol 76 (1) ◽

pp. 33-52 ◽

Cited By ~ 34

Author(s):

L Reuss ◽

S A Weinman ◽

T P Grady

Keyword(s):

Cell Membrane ◽

Amphotericin B ◽

Basolateral Membrane ◽

Membrane Potentials ◽

Equilibrium Potential ◽

Gallbladder Epithelium ◽

Bathing Medium ◽

Necturus Gallbladder ◽

Intracellular K Activity ◽

K Activity

A study of the mechanisms of the effects of amphotericin B and ouabain on cell membrane and transepithelial potentials and intracellular K activity (alpha Ki) of Necturus gallbladder epithelium was undertaken with conventional and K-selective intracellular microelectrode techniques. Amphotericin B produced a mucosa-negative change of transepithelial potential (Vms) and depolarization of both apical and basolateral membranes. Rapid fall of alpha Ki was also observed, with the consequent reduction of the K equilibrium potential (EK) across both the apical and the basolateral membrane. It was also shown that, unless the mucosal bathing medium is rapidly exchanged, K accumulates in the unstirred fluid layers near the luminal membrane generating a paracellular K diffusion potential, which contributes to the Vms change. Exposure to ouabain resulted in a slow decrease of alpha Ki and slow depolarization of both cell membranes. Cell membrane potentials and alpha Ki could be partially restored by a brief (3-4 min) mucosal substitution of K for Na. Under all experimental conditions (control, amphotericin B, and ouabain), EK at the basolateral membrane was larger than the basolateral membrane equivalent emf (Eb). Therefore, the K chemical potential difference appears to account for Eb and the magnitude of the cell membrane potentials, without the need to postulate an electrogenic Na pump. Comparison of the rate of Na transport across the tissue with the electrodiffusional K flux across the basolateral membrane indicates that maintenance of a steady-state alpha Ki cannot be explained by a simple Na,K pump-K leak model. It is suggested that either a NaCl pump operates in parallel with the Na,K pump, or that a KCl downhill neutral extrusion mechanism exists in addition to the electrodiffusional K pathway.

Download Full-text

Effect of sugars and amino acids on amphibian intestinal Cl- transport and intracellular Na+, K+, and Cl- activity

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1986.250.1.g109 ◽

1986 ◽

Vol 250 (1) ◽

pp. G109-G117

Author(s):

J. F. White ◽

K. Burnup ◽

D. Ellingsen

Keyword(s):

Cellular Level ◽

Equilibrium Potential ◽

Cl Transport ◽

Luminal Membrane ◽

Intracellular Na Activity ◽

The Difference ◽

Effect Of Glucose ◽

Intracellular K Activity ◽

Intestinal Ion Transport ◽

K Activity

The effect of glucose, galactose, and valine on intestinal Cl- transport and intracellular Cl-, Na+, and K+ activity was investigated in isolated segments of Amphiuma small intestine. By use of double-barreled Cl- -specific microelectrodes, it was observed that galactose and valine reduced the luminal membrane potential (psi m) and eliminated the difference between the Cl- equilibrium potential (ECl) and psi m, i.e., the Cl- accumulation potential (ECl-psi m) approached zero. Simultaneously, Cl- absorption (JnetCl) was reduced in short-circuited tissues and Na+ absorption was enhanced. In contrast, after exposure to glucose, psi m and ECl-psi m declined only transiently and JnetCl was unaltered. In tissues pretreated with galactose to reduce Cl- transport, addition of glucose to the serosal medium restored Cl- accumulation across the luminal membrane and the Cl- absorptive current. Glucose, galactose, and valine each reduced intracellular K+ activity significantly. Galactose and valine each increased [corrected] intracellular Na activity (aiNa) markedly, whereas glucose increased aiNa only slightly. In conclusion, intestinal ion transport can be limited by the availability of metabolic substrate. The nonmetabolized solutes galactose and valine inhibited Cl- uptake and net Cl- absorption while stimulating net Na absorption, as though net Na+ absorption has priority over Cl- transport at the cellular level. Cl- transport is reduced at both mucosal and serosal membranes. At the luminal membrane electrogenic Cl- uptake is slowed or a backleak of Cl- is enhanced; at the serosal membrane Cl- exchange with Na+ (and HCO3-) driven by the Na+ gradient is reduced. The availability of metabolizable glucose to the cell prevents the reduction in net Cl- absorption.

Download Full-text

Interaction between carbachol and vasoactive intestinal peptide in cells of isolated colonic crypts

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1992.262.5.g940 ◽

1992 ◽

Vol 262 (5) ◽

pp. G940-G944

Author(s):

L. Greenwald ◽

B. A. Biagi

Keyword(s):

Vasoactive Intestinal Peptide ◽

Chloride Transport ◽

Basolateral Membrane ◽

Distal Colon ◽

Equilibrium Potential ◽

Colonic Crypts ◽

Intracellular K Activity ◽

Crypt Cells ◽

Basolateral Membrane Potential ◽

K Activity

In a previous study [B. Biagi, Y.-Z. Wang, and H. J. Cooke, Am. J. Physiol. 258 (Gastrointest. Liver Physiol. 21): G223-G230, 1990], carbachol stimulated active chloride transport in rabbit distal colon, yet had no effect on the basolateral membrane potential (Vbl) of cells from isolated crypts from the same tissue. In the present study, crypt cells were first depolarized with vasoactive intestinal peptide (VIP; 1 x 10(-9) M) (control Vbl = -62 mV; VIP Vbl = -48 mV) and then exposed to carbachol in the presence of VIP. The VIP-induced depolarization of Vbl was completely reversed by carbachol (0.1 mM; repolarization to -65 mV). Similar repolarization was seen by applying carbachol to crypt cells depolarized by 10 mM aminophylline. Intracellular K+ activity (aiK), measured with K(+)-selective microelectrodes, was 64.3 mM (concn = 85 mM), yielding a K+ equilibrium potential (EK+) of -76 mV. Neither carbachol nor VIP application caused significant changes in aiK. These results demonstrate the presence of cholinergic receptors on colonic crypt cells. The magnitude of the carbachol effect on Vbl is greater when Vbl is depolarized relative to EK+. The results are consistent with the hypothesis that carbachol acts by increasing basolateral K+ conductance, driving the cell toward the EK+.

Download Full-text

Association between HCO3(-) absorption and K+ uptake by Amphiuma jejunum: relations among HCO3(-) absorption, luminal K+, and intracellular K+ activity

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1984.246.6.g732 ◽

1984 ◽

Vol 246 (6) ◽

pp. G732-G744

Author(s):

M. A. Imon ◽

J. F. White

Keyword(s):

Short Circuit ◽

Short Circuit Current ◽

Uptake Mechanism ◽

Bathing Medium ◽

The Media ◽

Absorptive Flux ◽

Free Media ◽

Intracellular K Activity ◽

K Activity

Titration techniques and K+- sensitive microelectrodes have been used to investigate the relations among HCO3(-) absorption, luminal K+, and intracellular K+ activity in in vitro Amphiuma jejunum. The HCO3(-) absorptive flux (JHCO3(-] measured by pH-stat under short circuit was reduced by removal of K+ from the medium but not by replacement of Na+ with choline. JHCO3(-) exhibited a seasonal variation when K+ was absent from the media and was increased to a maximum when K+ equaled 5 mM. Addition of K+ to a K+-free luminal medium stimulated JHCO3(-) much more than addition to the serosal medium. Acetazolamide (10(-4) M) blocked K+-stimulated HCO3(-) absorption while benzolamide reduced the short-circuit current associated with HCO3(-) absorption much more rapidly when added to the mucosal bathing medium. Intracellular K+ activity (aik) and mucosal membrane potential (psi m) of jejunal villus cells were measured with double-barreled microelectrodes. When bathed bilaterally with HCO3(-)-containing media, K+ was actively accumulated for many hours (aik = 58.5 mM) but in the presence of ouabain fell to equilibrium (16 mM) after 2 h. In contrast, when HCO3(-) absorption was induced by removal of serosal HCO3(-), aik was elevated to 83.6 mM and, after 4-h exposure to ouabain cell K+, remained far above electrochemical equilibrium at 33 mM. Tissues bathed in Na+-free (Tris) media containing ouabain retained cell K+ after 4 h at even higher levels (46 mM). Cell K+ activity was reduced by removal of K+ from either the mucosal or serosal medium. Acetazolamide reduced aik over 2 h in Na+-free media from 66 to 42 mM. The decline in aik was associated with a concomitant decline in the HCO3(-) absorptive current. It is concluded that K+ is actively accumulated across both luminal and serosal membranes of the jejunal absorptive cell and that the luminal uptake mechanism is linked to HCO3(-) absorption or an equivalent process.

Download Full-text

Basal membrane uptake in potassium-secreting cells of midgut of tobacco hornworm (Manduca sexta)

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1990.258.1.r112 ◽

1990 ◽

Vol 258 (1) ◽

pp. R112-R119

Author(s):

A. C. Chao ◽

A. R. Koch ◽

D. F. Moffett

Keyword(s):

Manduca Sexta ◽

Short Circuit ◽

Short Circuit Current ◽

Basal Membrane ◽

Bathing Solution ◽

K Uptake ◽

Active Secretion ◽

Uptake Process ◽

Intracellular K Activity ◽

K Activity

Basal membrane voltage (Vb), intracellular K+ activity [(K+)i], and short-circuit current (Isc) were measured in isolated posterior midguts of Manduca sexta wherein Isc is a measured of active secretion of K+ from blood into lumen. When bathed in 32 mM K+ and exposed to 100% O2, average values were Isc = 244 microAmp/cm2, Vb = -33.1 mV, and (K+)i = 88.6 mM. The electrochemical gradient across the basal membrane (d mu) averaged +5.8 mV (a gradient favorable for K+ entry). Exposure to 5% O2 led to a new steady state in which Isc = 71 microAmp/cm2, Vb = -18.7 mV, and (K+)i = 99.4 mM. During hypoxia, d mu averaged -9.9 mV (a gradient unfavorable for K+ entry). When the external bathing solution was 10 mM K+, comparable values were, for 100% O2, Isc = 139 microAmp/cm2, Vb = -56.1 mV, (K+)i = 72.2 mM, and d mu = +3.6 mV, and in 5% O2 the values were Isc = 28.3 microAmp/cm2, Vb = -43.7 mV, (K+)i = 76.1 mM, and d mu = -10.2 mV. The failure of cellular K+ to fall during prolonged hypoxia is evidence for a thermodynamically active basal K+ uptake process.

Download Full-text