Active K transport across rabbit distal colon: relation to Na absorption and Cl secretion

1986 ◽  
Vol 251 (2) ◽  
pp. C252-C267 ◽  
Author(s):  
D. R. Halm ◽  
R. A. Frizzell
Keyword(s):  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Secretory Process ◽  
Cl Secretion ◽  
K Secretion ◽  
Transport Inhibitors ◽  
Unidirectional Fluxes ◽  
K Transport

We measured isotopic unidirectional fluxes of K to elucidate the mechanisms of active K transport across the distal colon of the rabbit. Separate pathways for active K absorption and active K secretion were detected using various transport inhibitors and stimulators. The rate and direction of net K transport depend on the activities of these two pathways. K absorption was reduced by orthovanadate (both solutions) or serosal Ba, consistent with ATPase-dependent uptake of K across the apical membrane and exit via a Ba-sensitive basolateral K conductance. K secretion was inhibited by serosal ouabain or mucosal Ba, indicating that K secretion involves basolateral uptake via the Na-K pump and apical exit via a Ba-sensitive K conductance. Active K secretion appears to be electrogenic, since inhibition by ouabain produced equivalent changes in the net K flux and short-circuit current. Addition of bumetanide to the serosal solution or the removal of either Na or Cl from the serosal solution inhibited K secretion; mucosal solution amiloride was without effect. These results indicate that this K secretory process is independent of electrogenic Na absorption but is mechanistically similar to Cl secretory processes. Both epinephrine and prostaglandin E2 (PGE2) stimulate K secretion, but only PGE2 also stimulates Cl secretion. The response to these secretogogues suggests that the mechanisms underlying K and Cl secretion are closely linked but can be regulated independently.

Extracellular ATP stimulates K+ secretion across cultured human airway epithelium

1997 ◽  
Vol 272 (6) ◽  
pp. L1084-L1091 ◽  
Author(s):  
L. L. Clarke ◽  
T. Chinet ◽  
R. C. Boucher
Keyword(s):  
Airway Epithelium ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Extracellular Atp ◽  
Cl Secretion ◽  
Human Airway ◽  
Human Airway Epithelium ◽  
K Secretion

Extracellular ATP applied to the luminal side of human airway epithelium (HAE) activates an apical membrane Cl- conductance and transepithelial Cl- secretion. However, in some HAE preparations, we have found that luminal ATP induces a change in short-circuit current (Isc), consistent with K+ secretion. Using intracellular microelectrodes and radioisotopic flux studies, we investigated whether extracellular ATP regulates transepithelial K+ secretion in primary HAE cultures. In physiological Ringer solution, HAE had a negligible electrochemical driving force for Cl- secretion (DFCl), and luminal ATP induced a change in Isc opposite in polarity to Cl- secretion. Intracellular microelectrode measurements indicated that the "reversed" Isc was associated with activation of a hyperpolarizing (K+) conductance in the apical membrane. Radioisotope studies of HAE pretreated with amiloride to induce a favorable DFCl revealed that luminal ATP stimulates a small 42K secretory flux concurrently with Cl- secretion. In ion-substituted Ringer solution, luminal ATP stimulated both the outward (K+) current and the inward (Cl-) current with approximately equal potency (approximately 10(-6) M). We conclude that luminal ATP activates an apical membrane K+ conductance and transepithelial K+ secretion across HAE.

scholarly journals Role of the BK channel (KCa1.1) during activation of electrogenic K+ secretion in guinea pig distal colon

2012 ◽  
Vol 303 (12) ◽  
pp. G1322-G1334 ◽  
Author(s):  
Jin Zhang ◽  
Susan T. Halm ◽  
Dan R. Halm
Keyword(s):  
Guinea Pig ◽  
Apical Membrane ◽  
Splice Variants ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Bk Channel ◽  
Prostaglandin E ◽  
Maximal Inhibition ◽  
K Secretion

Secretagogues acting at a variety of receptor types activate electrogenic K+ secretion in guinea pig distal colon, often accompanied by Cl− secretion. Distinct blockers of KCa1.1 (BK, Kcnma1), iberiotoxin (IbTx), and paxilline inhibited the negative short-circuit current ( Isc) associated with K+ secretion. Mucosal addition of IbTx inhibited epinephrine-activated Isc (epi Isc) and transepithelial conductance (epi Gt) consistent with K+ secretion occurring via apical membrane KCa1.1. The concentration dependence of IbTx inhibition of epi Isc yielded an IC50 of 193 nM, with a maximal inhibition of 51%. Similarly, IbTx inhibited epi Gt with an IC50 of 220 nM and maximal inhibition of 48%. Mucosally added paxilline (10 μM) inhibited epi Isc and epi Gt by ∼50%. IbTx and paxilline also inhibited Isc activated by mucosal ATP, supporting apical KCa1.1 as a requirement for this K+ secretagogue. Responses to IbTx and paxilline indicated that a component of K+ secretion occurred during activation of Cl− secretion by prostaglandin-E2 and cholinergic stimulation. Analysis of KCa1.1α mRNA expression in distal colonic epithelial cells indicated the presence of the ZERO splice variant and three splice variants for the COOH terminus. The presence of the regulatory β-subunits KCaβ1 and KCaβ4 also was demonstrated. Immunolocalization supported the presence of KCa1.1α in apical and basolateral membranes of surface and crypt cells. Together these results support a cellular mechanism for electrogenic K+ secretion involving apical membrane KCa1.1 during activation by several secretagogue types, but the observed K+ secretion likely required the activity of additional K+ channel types in the apical membrane.

K+ transport by rat colon: adaptation to a low potassium diet

1986 ◽  
Vol 250 (3) ◽  
pp. F483-F487
Author(s):  
R. L. Tannen ◽  
R. Marino ◽  
D. C. Dawson
Keyword(s):  
Rat Kidney ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Rat Colon ◽  
High K ◽  
Isotope Technique ◽  
K Secretion ◽  
Low K ◽  
K Transport

Recent studies with the isolated perfused rat kidney have demonstrated the existence of an intrinsic renal adaptation to conserve K+ in response to ingestion of a low K+ diet for 3 days. To determine whether the colon alters its K+ transport properties in a similar fashion, we measured transmural 86Rb fluxes across sheets of distal colonic epithelium under short-circuit conditions. Preliminary studies using a double-isotope technique demonstrated that 86Rb and 42K fluxes were similar; therefore 86Rb flux was considered equivalent to K+ flux. The distal half of the colon from each rat was divided into two segments, referred to as early and late distal colon. Experiments were carried out using rats fed a K+ -free, control (0.15 mmol/g), and high K+ (1.13 mmol/g) powdered diet of otherwise identical electrolyte content. Net K+ secretion (Jnet) by the early distal colon was reduced from 0.45 in the controls to -0.02 mueq X cm-2 X h-1 by a low K+ diet as a result of a decrease in serosal-to-mucosal flux (Jsm), with no change in mucosal-to-serosal flux (Jms). Conductance (GT) and short-circuit current (Isc) were unchanged. Jnet by the late distal colon averaged 0.17 in the controls and 0.01 mueq X cm-2 X h-1 with a low K+ diet, but this difference was not significant statistically. In comparison with the controls, a high K+ diet had no effect on Jnet by the early distal colon (0.48 mueq X cm-2 X h-1) but increased Jnet by the late distal colon substantially (0.77 mueq X cm-2 X h-1).(ABSTRACT TRUNCATED AT 250 WORDS)

cGMP and Ca2+ regulation of ion transport across the isolated porcine distal colon epithelium

1994 ◽  
Vol 267 (4) ◽  
pp. R1026-R1033 ◽  
Author(s):  
M. D. DuVall ◽  
S. M. O'Grady
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Ussing Chambers ◽  
Cl Secretion ◽  
Nacl Absorption ◽  
Flux Measurements ◽  
K Secretion ◽  
Baseline Values ◽  
Distal Colon Epithelium

Intact epithelium from the porcine distal colon was stripped of serosal muscle and mounted in Ussing chambers to investigate the regulation of Na, Cl, and K transport by guanosine 3',5'-cyclic monophosphate (cGMP) and elevations in intracellular [Ca2+]. Under voltage-clamped conditions cGMP (250 microM) produced an increase in tissue short-circuit current (Isc) that reached a maximal value within 10-20 min and remained elevated > 40 min. This response was associated with an inhibition of NaCl absorption and stimulation of Cl and K secretion. In the absence of Cl the Isc also slowly increased but returned to baseline values within 20 min. Bicarbonate removal from both serosal and mucosal solutions or serosal bumetanide (20 microM) reduced the effect of cGMP on Isc by approximately 40%. When performed simultaneously, these conditions reduced the cGMP response by approximately 60%. Transepithelial Na and Cl flux measurements indicated that serosal bumetanide blocked increased Cl secretion without effecting changes in NaCl absorption. In contrast, mucosal amiloride blocked the effects of cGMP on NaCl absorption but not Cl secretion. The cGMP Isc response was potentiated in the presence of 1 mM, but not 10 microM, amiloride. Moreover, 1 mM amiloride inhibited Isc under control conditions but was ineffective in the presence of cGMP. The Ca2+ ionophore ionomycin (3 microM) produced a transient increase in the Isc that was also associated with a decrease in transepithelial NaCl absorption and an increase in Cl and K secretion. In contrast to cGMP, the ionomycin Isc response was eliminated after Cl removal from the bath.(ABSTRACT TRUNCATED AT 250 WORDS)

Dihydroxy bile salt-induced secretion of rubidium ion across the rabbit distal colon

1987 ◽  
Vol 252 (4) ◽  
pp. G554-G561 ◽  
Author(s):  
R. W. Freel
Keyword(s):  
Bile Salt ◽  
Short Circuit ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Distal Colon ◽  
Simultaneous Measurements ◽  
K Secretion ◽  
Unidirectional Fluxes ◽  
Highly Correlated ◽  
K Transport

Possible mechanisms of dihydroxy bile salt-induced K+ secretion by the mammalian colon were evaluated by studying the effects of taurochenodeoxycholate (TCDC) on 86Rb+ transport across the isolated, short-circuited rabbit distal colon. Simultaneous measurements of 86Rb+ and 42K+ unidirectional fluxes were highly correlated [r = 0.964 for serosal (s) to mucosal (m) and 0.765 for m to s], indicating that Rb+ is a suitable tracer for K+ transport across the colon. Furthermore, mucosal Ba2+ (4 mM) or serosal ouabain (0.1 mM) decreased serosal to mucosal rubidium flux (JRbs----m) (from 0.24 +/- 0.02 to 0.09 +/- 0.02, and 0.08 +/- 0.01 mu eq X h-1 X cm-2, respectively) without affecting JRbm----s. Dibutyryl cyclic adenosine monophosphate (dBcAMP, 0.5 mM serosal) specifically increased JRbs----m of controls (from 0.21 +/- 0.05 to 0.67 +/- 0.09 mu eq X h-1 X cm-2) through a barium- (4 mM, mucosal) sensitive pathway without affecting JRbs----m. Mucosal addition of 2 mM TCDC increased tissue conductance (GT), reduced short-circuit (Isc) slightly, and reversed JRbnet (from 0.13 +/- 0.05 to -0.29 +/- 0.08 mu eq X h-1 X cm-2) principally by increasing JRbs----m. The TCDC-induced increases in JRbs----m were reduced by 0.1 mM serosal ouabain (from 0.53 +/- 0.03 to 0.11 +/- 0.02 mu eq X h-1 X cm-2) or 4 mM mucosal Ba2+ (from 0.76 +/- 0.07 to 0.32 +/- 0.04 mu eq X h-1 X cm-2).(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Prostanoids stimulate K secretion and Cl secretion in guinea pig distal colon via distinct pathways

2001 ◽  
Vol 281 (4) ◽  
pp. G984-G996 ◽  
Author(s):  
Dan R. Halm ◽  
Susan Troutman Halm
Keyword(s):  
Guinea Pig ◽  
Rank Order ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Prostanoid Receptors ◽  
Cl Secretion ◽  
Inflammatory Conditions ◽  
K Secretion

Short-circuit current ( I sc) and transepithelial conductance ( G t) were measured in guinea pig distal colonic mucosa isolated from submucosa and underlying muscle layers. Indomethacin (2 μM) and NS-398 (2 μM) were added to suppress endogenous production of prostanoids. Serosal addition of PGE2 (10 nM) stimulated negative I scconsistent with K secretion, and concentrations >30 nM stimulated positive I sc consistent with Cl secretion. PGE2 also stimulated G t at low and high concentrations. Dose responses to prostanoids specific for EP prostanoid receptors were consistent with stimulating K secretion through EP2 receptors, based on a rank order potency (from EC50 values) of PGE2 (1.9 nM) > 11-deoxy-PGE1 (8.3 nM) > 19( R)-hydroxy-PGE2 (13.9 nM) > butaprost (67 nM) > 17-phenyl-trinor-PGE2 (307 nM) ≫ sulprostone (>10 μM). An isoprostane, 8-iso-PGE2, stimulated K secretion with an EC50 of 33 nM. Cl secretory response was stimulated by PGD2 and BW-245C, a DP prostanoid receptor-specific agonist: BW-245C (15 nM) > PGD2 (30 nM) > PGE2 (203 nM). Agonists specific for FP, IP, and TP prostanoid receptors were ineffective in stimulating I sc and G t at concentrations <1 μM. These results indicate that PGE2stimulated electrogenic K secretion through activation of EP2 receptors and electrogenic KCl secretion through activation of DP receptors. Thus stimulation of Cl secretion in vivo would occur either via physiological concentrations of PGD2(<100 nM) or pathophysiological concentrations of PGE2(>100 nM) that could occur during inflammatory conditions.

Bovine and porcine large intestine as model epithelia in a student lab course.

1993 ◽  
Vol 265 (6) ◽  
pp. S10 ◽  
Author(s):  
U Hegel ◽  
M Fromm ◽  
K M Kreusel ◽  
M Wiederholt
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Secretory Diarrhea ◽  
Tissue Preparation ◽  
Cl Secretion ◽  
Animal Physiology ◽  
Daily Schedule ◽  
K Secretion ◽  
Transepithelial Voltage

A short-circuit current experiment on epithelial ion transport is described that is suitable for student classes in human and animal physiology. Segments of late distal colon from either pig or cow are obtained from the slaughterhouse depending on the animals' daily schedule. Initial tissue preparation already in the slaughterhouse, cold storage, and proper choice of bath solutions are essential prerequisites for success. Students monitor spontaneous transepithelial voltage and short-circuit current (Isc) by use of manually operated voltage clamp units. Two main transport mechanisms are studied, electrogenic Na+ absorption and Cl- secretion. Electrogenic Na+ absorption is studied by measuring the Isc drop after amiloride. Then Cl- secretion is stimulated by theophylline and subsequently inhibited by furosemide. In some experiments K+ secretion can be detected by the blocking effect of mucosal Ba2+. Response of tissues from pig and cow is qualitatively similar but quantitatively different. The equipment is sturdy and inexpensive, can be provided by most departmental workshops, and has been tested for 3 yr in regular lab courses. Observations made during these experiments are closely related to clinical states, such as secretory diarrhea, cystic fibrosis, and hyperaldosteronism, as well as to the mechanisms of clinically used diuretics.

Apical nonspecific cation conductances in rabbit cecum

1994 ◽  
Vol 266 (3) ◽  
pp. G475-G484 ◽  
Author(s):  
J. H. Sellin ◽  
W. P. Dubinsky
Keyword(s):  
Epithelial Transport ◽  
Apical Membrane ◽  
Divalent Cations ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Na Channel ◽  
Similar Response ◽  
Electrogenic Transport

Rabbit cecum exhibits electrogenic Na absorption in vitro. However, because this transport process is not inhibited by amiloride nor does it demonstrate saturation kinetics typical of the amiloride-inhibitable Na channel, we considered whether the cecal transporter represented one of a recently described family of nonselective cation conductances or channels (NSCC). Both transepithelial and vesicle studies demonstrated that K, Cs, and Rb were transported via an apical conductance. Electrogenic transport was inhibited by divalent cations including Ca, Mg, and Ba but was unaffected by either lanthanum or gadolinium. Parallel studies in distal colon did not exhibit a similar response to either K substitution or Ba inhibition. Phenamil, verapamil, and nicardipine significantly inhibited the short-circuit current (Isc). stimulated by nominal Ca- and Mg-free conditions. Flux studies demonstrated a correlation between changes in Isc and Na transport. Microelectrode impalement studies suggested that there may be both NSCC and K conductance in the apical membrane. Planar bilayer studies identified a 190-pS cation channel that may correlate with the macroscopic transport properties of this epithelium. These studies are consistent with a model of cecal Na absorption mediated by a NSCC in the apical membrane; this may be the mechanism underlying the distinct epithelial transport characteristics of this intestinal segment.

Role of calcium in chloride secretion mediated by cAMP pathway activation in rabbit distal colon mucosa

1993 ◽  
Vol 264 (2) ◽  
pp. G252-G260 ◽  
Author(s):  
V. Calderaro ◽  
E. Chiosi ◽  
R. Greco ◽  
A. M. Spina ◽  
A. Giovane ◽  
...  
Keyword(s):  
Short Circuit ◽  
Fold Increase ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Chloride Secretion ◽  
Free Medium ◽  
Cl Secretion ◽  
Pathway Activation ◽  
Flux Measurements ◽  
Pg E2

Effects of Ca2+ on adenosine 3',5'-cyclic monophosphate (cAMP)-mediated Cl- secretion were investigated in intact mucosa and isolated crypt cells of rabbit descending colon. Addition of 10 microM prostaglandin (PG)E2 or forskolin to tissues incubated in Ca(2+)-free medium increased the size of short-circuit current (Isc) and Cl- secretion as estimated by unidirectional 36Cl flux measurements (net flux = -2.31 +/- 0.24 vs. -1.22 +/- 0.10 mueq.h-1.cm-2, n = 4, P < 0.001). Addition of 10 microM PGE2 to tissues incubated in 1.2 mM Ca2+ Ringer induced a 7-fold increase in mean cAMP level, whereas it produced an 11-fold increase in tissues exposed to Ca(2+)-free medium. Membrane preparations from whole mucosa incubated in Ca(2+)-free medium displayed a cyclic nucleotide phosphodiesterase activity significantly lower than controls (18.76 +/- 0.54 vs. 31.20 +/- 0.39 pmol cAMP. mg protein-1.min-1, means +/- SE, n = 4, P < 0.001). Ca2+ removal also affected adenylate cyclase (AC) responsiveness to agonists; AC activity increased in controls by 54 and 226% after stimulation with 10 microM PGE2 and forskolin, respectively, but it increased more (77 and 325%, respectively) after incubation in Ca(2+)-free solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

cAMP-dependent sulfate secretion by the rabbit distal colon: a comparison with electrogenic chloride secretion

1997 ◽  
Vol 273 (1) ◽  
pp. C148-C160 ◽  
Author(s):  
R. W. Freel ◽  
M. Hatch ◽  
N. D. Vaziri
Keyword(s):  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Chloride Secretion ◽  
Disulfonic Acid ◽  
Cl Secretion ◽  
Cyclic Monophosphate ◽  
Anion Conductance ◽  
Flux Measurements

The ability of a Cl-secreting epithelium to support net secretion of an anion other than a halide was investigated with 35SO4 flux measurements across the isolated, short-circuited rabbit distal colon. In most experiments, 36Cl fluxes were simultaneously measured to validate the secretory capacity of the tissues. Serosal addition of dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP, 0.5 mM) stimulated a sustained net secretion of SO4 (about -3.0 nmol.cm-2.h-1 from a 0.20 mM solution) via an increase in the serosal-to-mucosal unidirectional flux, whereas Ca ionophore A-23187 (1 microM, serosal) produced a more transient stimulation of SO4 and Cl secretion. Net adenosine 3',5'-cyclic monophosphate (cAMP)-dependent SO4 and Cl secretion were strongly voltage sensitive, principally through the potential dependence of the serosal-to-mucosal fluxes, indicating an electrogenic transport process. Symmetrical replacement of either Na, K, or Cl inhibited cAMP-dependent SO4 secretion, whereas HCO3-free buffers had no effect on SO4 secretion. Serosal bumetanide (50 microM) or furosemide (100 microM) reduced DBcAMP-stimulated SO4 and Cl secretion, whereas serosal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid or 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (50 microM) blocked DBcAMP-induced SO4 secretion while enhancing net Cl secretion and short-circuit current. Mucosal 5-nitro-2-(3-phenylpropylamino)benzoic acid partially inhibited SO4 secretion and completely inhibited Cl secretion. It is concluded that secretagogue-stimulated SO4 secretion, like Cl secretion, may be an electrogenic process mediated by diffusive efflux through an apical anion conductance. Cellular accumulation of SO4 across the basolateral membrane appears to be achieved by a mechanism that is distinct from that employed by Cl.

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