scholarly journals Mechanisms of K+ uptake across the basal membrane of malpighian tubules of Formica polyctena: the effect of ions and inhibitors.

1994 ◽  
Vol 195 (1) ◽  
pp. 123-145 ◽  
Author(s):  
A Leyssens ◽  
S Dijkstra ◽  
E Van Kerkhove ◽  
P Steels
Keyword(s):  
Membrane Potential ◽  
Electrical Potential ◽  
Basal Membrane ◽  
Fluid Secretion ◽  
Malpighian Tubules ◽  
K Uptake ◽  
Bathing Medium ◽  
K Channels ◽  
High K ◽  
K Concentration

In the presence of 6 mmol l-1 Ba2+, known to block the K+ channels in the basal membrane, a rise in bath [K+] ([K+]bl) induced an increase in intracellular K+ concentration ([K+]i) similar in amount and in time course to that obtained in the absence of Ba2+. The presence of active and passive (other than through K+ channels) K+ uptake mechanisms across the basal membrane was investigated in different bath K+ concentrations. Dihydro-ouabain (10(-3) mol l-1), a blocker of the Na+/K(+)-ATPase, tested in low bath [K+], and Sch28080 (10(-4) mol l-1), a K+/H(+)-ATPase inhibitor, were without effect on fluid secretion. Dihydro-ouabain was also without effect on electrical potential differences either in the absence or in the presence of Ba2+. Vanadate (10(-3) mol l-1), in contrast, strongly reduced fluid secretion not only in control solution but also in high-K+, Na(+)-free medium and reduced the transepithelial and the apical membrane potential differences but not the basal membrane potential difference of [K+]i. Omitting Na+ from the bathing medium, replacing Cl- by Br- or applying bumetanide (10(-5) mol l-1) inhibited fluid secretion only in a low-K+ (10 mmol l-1) medium. In 51 mmol l-1 [K+]bl, omitting Na+ was without effect and 10(-4) mol l-1 bumetanide was needed to inhibit secretion. Replacing Cl- by Br- stimulated fluid secretion at this K+ concentration. Bumetanide (10(-4) mol l-1) had no effect in 113 mmol l-1 [K+]bl. Bumetanide (10(-4) mol l-1) in 51 mmol l-1 [K+]bl did not affect membrane potentials, did not lower [K+]i and did not affect the rise in [K+]i observed on an increase in [K+]bl. The results were summarized in a model proposing that K+ channels play a dominant role in high-K+ (113 mmol l-1) bathing medium. A K+/Cl- cotransporter may become more important in 51 mmol l-1 [K+]bl and a K+/Na+/2Cl- cotransporter may gain in importance in 10 mmol l-1 [K+]bl. Active mechanisms for K+ uptake across the basal membrane seem to play no detectable role in sustaining fluid secretion. The response to vanadate might be due to an effect on the apical electrogenic H+ pump.

Transepithelial and intracellular potentials in isolated Malpighian tubules of tenebrionid beetle

1987 ◽  
Vol 252 (4) ◽  
pp. F645-F653 ◽  
Author(s):  
S. W. Nicolson ◽  
L. C. Isaacson
Keyword(s):  
Membrane Potential ◽  
Basal Membrane ◽  
Fluid Secretion ◽  
Malpighian Tubules ◽  
Bathing Medium ◽  
Intracellular Potentials ◽  
Tenebrionid Beetle ◽  
Fold Reduction ◽  
K Concentration ◽  
Opposing Effects

Malpighian tubules of Onymacris plana (Coleoptera: Tenebrionidae) have been isolated for measurement of transepithelial and intracellular potentials, before and during stimulation of fluid secretion. In a bathing medium resembling the hemolymph composition of the insect, the transepithelial potential (VT) was approximately 13 mV, lumen positive. VT was subject to drift and frequently showed super-imposed regular oscillations, which were apparently action potentials associated with contractions of muscle fibers running along the tubules. Although tubules of Onymacris are approximately 8 cm long, the basal membrane potential (Vb) did not vary with distance along the tubule, averaging -31 mV. Addition of adenosine 3',5'-cyclic monophosphate (cAMP) or diuretic hormone (DH) homogenate to the bathing medium had no effect on Vb, but opposing effects on VT: cAMP caused it to increase to 60 mV, whereas DH homogenate caused a rapid drop in VT to almost zero. Ion substitutions in the bathing medium showed that under control conditions beetle tubules possessed appreciable basal permeability to both K and Cl ions, with a 10-fold reduction in bath K concentration hyperpolarizing Vb by 54 mV. The basal K and Cl channels were partially blocked by barium and thiocyanate ions, respectively. Stimulation with cAMP increased the apical membrane potential (Va) and significantly reduced the Cl permeability of the basal membrane, whereas its Na permeability remained negligible.

scholarly journals Secretion by the Malpighian tubules of Rhodnius prolixus stal: electrical events

1984 ◽  
Vol 110 (1) ◽  
pp. 275-290 ◽  
Author(s):  
M. J. O'Donnell ◽  
S. H. Maddrell
Keyword(s):  
Apical Membrane ◽  
Electrical Response ◽  
Basal Membrane ◽  
Fluid Secretion ◽  
Malpighian Tubules ◽  
Chloride Permeability ◽  
Bathing Medium ◽  
Before And After ◽  
Electrical Gradient ◽  
Cation Pump

Transepithelial and intracellular potentials have been simultaneously recorded from Rhodnius upper Malpighian tubules before and after stimulation of fluid secretion. The transepithelial electrical response to the diuretic hormone mimic 5-hydroxytryptamine (5-HT) was triphasic; recordings of intracellular potential changes indicated that the three phases represented successive events at the apical membrane. Depolarizations produced by increasing the bathing medium potassium concentration indicated that the basal membrane was much more permeable to potassium than to sodium. Electrical responses to chloride-free saline were inconsistent with a significant basal membrane chloride permeability. Chloride movements across the basal membrane were opposed by an electrical gradient of about 65 mV. The results of experiments in which tubules were exposed to chloride-free saline or sodium-free saline suggested that chloride entry into the cells was linked to the entry of Na+ and K+. The effects of furosemide and bumetanide upon secretion and potential changes suggested that chloride crossed the basal membrane through co-transport with Na+ and K+. Chloride probably crosses the apical membrane into the lumen passively in response to a favourable electrical gradient of about 35 mV. Cations must be actively pumped into the lumen against an electrical gradient of 35 mV. Our results support previous evidence for an apical cation pump which actively transports Na and K into the lumen. A tentative model of ionic movements during fluid secretion is presented. It is suggested that the apical cation pump maintains sodium at low intracellular concentrations, thereby maintaining a favourable gradient for entry of Na+ through the proposed basal co-transport step. The suggested stoichiometry is Na+:K+:2 Cl-.

Electrophysiological and cable parameters of perfused beetle malpighian tubules

1989 ◽  
Vol 257 (5) ◽  
pp. R1190-R1198
Author(s):  
L. C. Isaacson ◽  
S. W. Nicolson ◽  
D. W. Fisher
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Fluid Secretion ◽  
Electrical Circuit ◽  
Malpighian Tubules ◽  
Luminal Diameter ◽  
High K ◽  
Length Constant ◽  
K Concentration ◽  
Coleoptera Tenebrionidae

Isolated perfused Malpighian tubules of the desert beetle Onymacris plana (Coleoptera: Tenebrionidae) have been subjected to cable analysis under the following conditions: control, adenosine 3',5'-cyclic monophosphate (cAMP), corpora cardiaca homogenate (CCH), and high ambient K (130 mM). In addition, we investigated possible effects of perfusate composition on proximal transtubular potential (Vo) by reducing K, Na, or Cl or by adding ouabain, furosemide, or dinitrophenol. The effects of cAMP, CCH, and high K on Vo and cable parameters were consistent with increased fluid secretion, i.e., diminished input and core resistances and increased virtual short-circuit current, length constant, and luminal diameter. They differed in that CCH had variable effects on Vo and high K did not reduce transepithelial resistance. In terms of their effects on the parameters of a simple equivalent electrical circuit, the responses to cAMP, CCH, and a high ambient K concentration appear to be mediated by different mechanisms. Alterations in perfusate composition were almost without effect.

Contributions of K+:Cl- cotransport and Na+/K+-ATPase to basolateral ion transport in malpighian tubules of Drosophila melanogaster

1999 ◽  
Vol 202 (11) ◽  
pp. 1561-1570 ◽  
Author(s):  
S.M. Linton ◽  
M.J. O'Donnell
Keyword(s):  
Drosophila Melanogaster ◽  
Membrane Potential ◽  
Cyclic Amp ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Fluid Secretion ◽  
Malpighian Tubules ◽  
Minor Role ◽  
Electrochemical Gradient ◽  
Tubule Cells

Mechanisms of Na+ and K+ transport across the basolateral membrane of isolated Malpighian tubules of Drosophila melanogaster were studied by examining the effects of ion substitution and putative inhibitors of specific ion transporters on fluid secretion rates, basolateral membrane potential and secreted fluid cation composition. Inhibition of fluid secretion by [(dihydroindenyl)oxy]alkanoic acid (DIOA) and bumetanide (10(−)4 mol l-1) suggested that a K+:Cl- cotransporter is the main route for K+ entry into the principal cells of the tubules. Differences in the effects of bumetanide on fluxes of K+ and Na+ are inconsistent with effects upon a basolateral Na+:K+:2Cl- cotransporter. Large differences in electrical potential across apical (>100 mV, lumen positive) and basolateral (<60 mV, cell negative) cell membranes suggest that a favourable electrochemical gradient for Cl- entry into the cell may be used to drive K+ into the cell against its electrochemical gradient, via a DIOA-sensitive K+:Cl- cotransporter. A Na+/K+-ATPase was also present in the basolateral membrane of the Malpighian tubules. Addition of 10(−)5 to 10(−)3 mol l-1 ouabain to unstimulated tubules depolarized the basolateral potential, increased the Na+ concentration of the secreted fluid by 50–73 % and increased the fluid secretion rate by 10–19 %, consistent with an increased availability of intracellular Na+. We suggest that an apical vacuolar-type H+-ATPase and a basolateral Na+/K+-ATPase are both stimulated by cyclic AMP. In cyclic-AMP-stimulated tubules, K+ entry is stimulated by the increase in the apical membrane potential, which drives K+:Cl- cotransport at a faster rate, and by the stimulation of the Na+/K+-ATPase. Fluid secretion by cyclic-AMP-stimulated tubules was reduced by 26 % in the presence of ouabain, suggesting that the Na+/K+-ATPase plays a minor role in K+ entry into the tubule cells. Malpighian tubules secreted a Na+-rich (150 mmol l-1) fluid at high rates when bathed in K+-free amino-acid-replete saline (AARS). Secretion in K+-free AARS was inhibited by amiloride and bafilomycin A1, but not by bumetanide or hydrochlorothiazide, which inhibit Na+:Cl- cotransport. There was no evidence for a Na+ conductance in the basolateral membrane of unstimulated or cyclic-AMP-stimulated tubules. Possible mechanisms of Na+ entry into the tubule cells include cotransport with organic solutes such as amino acids and glucose.

Studies on the mechanism of fluid secretion by isolated salivary glands of Calliphora

1976 ◽  
Vol 64 (2) ◽  
pp. 311-322
Author(s):  
M. J. Berridge ◽  
B. D. Lindley ◽  
W. T. Prince
Keyword(s):  
Salivary Glands ◽  
Apical Membrane ◽  
Potassium Concentration ◽  
Basal Membrane ◽  
Fluid Secretion ◽  
Sodium Permeability ◽  
Bathing Medium ◽  
Major Cation ◽  
Diuretic Agent ◽  
External Potassium

1. Potassium is the major cation in the secretion of the salivary glands of Calliphora and is necessary for full secretory rates. 2. Other ions (rubidium and sodium) can support secretion in the absence of potassium. 39. During stimulation with 5-HT a Nernst plot of the basal membrane potential has a slope of 53 mV for a tenfold change in external potassium concentration and the slope at rest deviates from this over the range I-20 mM external potassium. 4. Hyperpolarization of the basal membrane by 5-HT is abolished if the chloride in the bathing medium is replaced by isethionate. 5. The diuretic agent amiloride inhibits fluid secretion by a mechanism which may include a reduction in calcium entry in addition to its recognized effect on sodium permeability. 6. A model is proposed in which fluid secretion is driven by the active transport of potassium across the apical membrane with chloride following passively.

THE EFFECTS OF MANDUCA SEXTA DIURETIC HORMONE ON FLUID TRANSPORT BY THE MALPIGHIAN TUBULES AND CRYPTONEPHRIC COMPLEX OF MANDUCA SEXTA

1993 ◽  
Vol 178 (1) ◽  
pp. 231-243 ◽  
Author(s):  
N. Audsley ◽  
G. M. Coast ◽  
D. A. Schooley
Keyword(s):  
Cyclic Amp ◽  
Manduca Sexta ◽  
Fluid Transport ◽  
Basal Membrane ◽  
Fluid Secretion ◽  
Hormonal Control ◽  
Malpighian Tubules ◽  
Proximal Tubules ◽  
Fluid Absorption ◽  
Diuretic Hormone

1. Manduca sexta diuretic hormone (Mas-DH) stimulates fluid secretion by adult Malpighian tubules of M. sexta, demonstrating its site of diuretic action in M. sexta for the first time. It was not possible to develop a suitable bioassay to measure fluid secretion in larval proximal tubules. 2. Mas-DH has an antidiuretic action on the cryptonephric complex of larval M. sexta because it increases fluid absorption from the rectum. It appears that in this complex Mas-DH is acting on a Na+/K+/2Cl- co-transporter, presumably on the basal membrane of the cryptonephric Malpighian tubules, because Mas-DH-stimulated fluid absorption by the cryptonephric complex is inhibited by bumetanide or the removal of Cl-, Na+ or K+ from the haemolymph side of the tissue. This is the first demonstration of hormonal control of fluid absorption by the cryptonephric complex. 3. Concomitant with the stimulation of fluid transport, Mas-DH increases the amount of cyclic AMP secreted by adult Malpighian tubules and the cryptonephric complex. In addition, Mas-DH promotes cyclic AMP production by the larval proximal tubules.

Potassium distribution and membrane potential of sensory neurons in the leech nervous system

1984 ◽  
Vol 51 (4) ◽  
pp. 689-704 ◽  
Author(s):  
W. R. Schlue ◽  
J. W. Deitmer
Keyword(s):  
Nervous System ◽  
Membrane Potential ◽  
Sensory Neurons ◽  
Membrane Resistance ◽  
Equilibrium Potential ◽  
Bathing Medium ◽  
Membrane Hyperpolarization ◽  
K Concentration ◽  
Intracellular K Activity ◽  
K Activity

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)

Dibutyryl-cAMP increases basolateral sodium conductance of mosquito Malpighian tubules

1985 ◽  
Vol 248 (3) ◽  
pp. R339-R345 ◽  
Author(s):  
D. B. Sawyer ◽  
K. W. Beyenbach
Keyword(s):  
Basolateral Membrane ◽  
Fold Increase ◽  
Fluid Secretion ◽  
Malpighian Tubules ◽  
Dibutyryl Camp ◽  
Dominant Effect ◽  
Membrane Conductances ◽  
Transepithelial Voltage ◽  
K Concentration ◽  
Basolateral Membrane Potential

Dibutyryladenosine 3',5'-cyclic monophosphate (cAMP) stimulates fluid secretion in isolated Malpighian tubules of the mosquito Aedes aegypti. In the present study the effects of cAMP on the basolateral membrane were studied with conventional microelectrodes. Membrane conductances were evaluated from the changes of the basolateral membrane potential (Vbl) consequent to ion changes in the bath. Under control conditions, Vbl measured -65.2 +/- 1.5 mV [83 impalements, 67 tubules]. A fivefold decrease in the bath Na concentration hyperpolarized Vbl by 10.2 +/- 0.6 mV [7], whereas a 4.4-fold increase in the bath K concentration depolarized Vbl by 7.9 +/- 1.0 mV [9]. In the presence of cAMP (10(-4) M) Vbl depolarized to -24.8 +/- 2.7 mV [9]. Vbl now hyperpolarized by 22.7 +/- 1.5 mV [7] for the bath Na change and depolarized by only 3.8 +/- 1.1 mV [6] for the bath K change. Thus the dominant effect of cAMP is the increase of the basolateral membrane Na conductance. This increase is consistent with 1) the depolarization of Vbl and 2) the hyperpolarization of the transepithelial voltage, the decrease of the transepithelial resistance, and the increase of Na and fluid secretion observed previously. Spontaneous oscillations of Vbl were observed and could not be attributed to cyclical changes of the basolateral membrane Na conductance.

scholarly journals Electrophysiology of flounder intestinal mucosa. I. Conductance properties of the cellular and paracellular pathways.

1985 ◽  
Vol 85 (6) ◽  
pp. 843-864 ◽  
Author(s):  
D R Halm ◽  
E J Krasny ◽  
R A Frizzell
Keyword(s):  
Membrane Potential ◽  
Apical Membrane ◽  
Driving Forces ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Membrane Conductance ◽  
Equivalent Circuit Analysis ◽  
K Secretion ◽  
Paracellular Pathways ◽  
K Concentration

We evaluated the conductances for ion flow across the cellular and paracellular pathways of flounder intestine using microelectrode techniques and ion-replacement studies. Apical membrane conductance properties are dominated by the presence of Ba-sensitive K channels. An elevated mucosal solution K concentration, [K]m, depolarized the apical membrane potential (psi a) and, at [K]m less than 40 mM, the K dependence of psi a was abolished by 1-2 mM mucosal Ba. The basolateral membrane displayed Cl conductance behavior, as evidenced by depolarization of the basolateral membrane potential (psi b) with reduced serosal Cl concentrations, [Cl]s. psi b was unaffected by changes in [K]s or [Na]s. From the effect of mucosal Ba on transepithelial K selectivity, we estimated that paracellular conductance (Gp) normally accounts for 96% of transepithelial conductance (Gt). The high Gp attenuates the contribution of the cellular pathway to psi t while permitting the apical K and basolateral Cl conductances to influence the electrical potential differences across both membranes. Thus, psi a and psi b (approximately 60 mV, inside negative) lie between the equilibrium potentials for K (76 mV) and Cl (40 mV), thereby establishing driving forces for K secretion across the apical membrane and Cl absorption across the basolateral membrane. Equivalent circuit analysis suggests that apical conductance (Ga approximately equal to 5 mS/cm2) is sufficient to account for the observed rate of K secretion, but that basolateral conductance (Gb approximately equal to 1.5 mS/cm2) would account for only 50% of net Cl absorption. This, together with our failure to detect a basolateral K conductance, suggests that Cl absorption across this barrier involves KCl co-transport.

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