Forskolin effects on frog and rabbit corneal epithelium ion transport

1986 ◽  
Vol 251 (3) ◽  
pp. C448-C454 ◽  
Author(s):  
O. A. Candia ◽  
L. R. Grillone ◽  
T. C. Chu
Keyword(s):  
Corneal Epithelium ◽  
Rana Catesbeiana ◽  
Apical Membrane ◽  
Short Circuit ◽  
Control Level ◽  
Short Circuit Current ◽  
Potential Difference ◽  
Ionophore A23187 ◽  
Intracellular Recordings ◽  
Stimulation Of

The effects of forskolin on the electrophysiological parameters of the isolated corneal epithelium from bullfrog (Rana catesbeiana) were investigated. Forskolin stimulated the short-circuit current (SCC) and transepithelial potential difference (PDt), while reducing the transepithelial resistance. These effects were absent in Cl- -free bathing solutions. Furosemide, added either before or after forskolin, completely blocked the effects. Epinephrine and A23187, added after forskolin, produced only a small additional stimulation of the SCC. Propranolol neither blocked nor reduced the effect of forskolin. Forskolin increased the stroma to tear 36Cl flux by 61% and the tear to stroma 36Cl flux by 64%. Intracellular recordings showed that forskolin depolarized the potential difference across the apical membrane and reduced the apical/basolateral resistance ratio. Intracellular recordings in the isolated rabbit epithelium showed the same effects by forskolin except that there was only a brief stimulation of PDt, after which it stabilized slightly below the control level. These results are consistent with an increase in apical membrane permeability similar to that produced by adenosine 3',5'-cyclic monophosphate, epinephrine, and the Ca2+ ionophore A23187.

Forskolin-induced HCO3- current across apical membrane of the frog corneal epithelium

1990 ◽  
Vol 259 (2) ◽  
pp. C215-C223 ◽  
Author(s):  
O. A. Candia
Keyword(s):  
Corneal Epithelium ◽  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Pump Current ◽  
Gas Composition ◽  
Apical Side ◽  
Disulfonic Stilbene ◽  
Stimulation Of

Forskolin (and other Cl- secretagogues) does not affect the very small Na(+)-originated short-circuit current (Isc) across frog corneal epithelium bathed in Cl- free solutions. However, forskolin in combination with increased PCO2 bubbling of the solutions (5-20% CO2) stimulated Isc proportionally to PCO2 to a maximum of approximately 8 microA/cm2. This current could be eliminated and reinstated by sequentially changing the gas composition of the bubbling to 100% air and 20% CO2-80% air. The same effects were observed when PCO2 changes were limited to the apical-side solution. Stroma-to-tear HCO3- movement was deemed unlikely, since the increase in Isc was observed with a HCO3(-)-free solution on the stromal side and CO2 gassing limited to the tear side. From the effects of ouabain and tryptamine, at least 80% of the Isc across the basolateral membrane can be accounted for by the Na+ pump current plus K+ movement from cell to bath. Methazolamide also inhibited Isc. Current across the apical membrane cannot be attributed to an electronegative Na(+)-HCO3- symport given the insensitivity of Isc to a disulfonic stilbene and the fact that stroma-to-tear Na+ fluxes did not increase on stimulation of Isc. The tear-to-stroma Na+ flux also remained unaltered, negating an increased apical bath-to-cell Na+ flow. The forskolin-20% CO2 manipulation produced a depolarization of the intracellular potential, a reduction in the apical-to-basolateral resistance ratio, and a decrease in transepithelial resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of alpha 1- and alpha 2-adrenergic receptors in Cl- transport across frog corneal epithelium

1988 ◽  
Vol 255 (6) ◽  
pp. C724-C730 ◽  
Author(s):  
T. C. Chu ◽  
O. A. Candia
Keyword(s):  
Adenylate Cyclase ◽  
Corneal Epithelium ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Negative Influence ◽  
Adenylate Cyclase System ◽  
Positive Effects ◽  
Cl Transport ◽  
Beta Agonists

Norepinephrine, 10(-6) M, reduced Cl- transport by 26% in 75% of isolated frog corneal epithelia. This inhibition was not previously reported. Since beta-adrenergic agonists are known to only stimulate Cl- transport, the action of specific alpha 1- and alpha 2-agonists on Cl- transport and electrical parameters was investigated. Phenylephrine, an alpha 1-agonist always stimulated the Cl(-)-dependent short-circuit current (Isc), but less than the beta-agonists. UK-14,304-18 (UK), a selective alpha 2-agonist, reduced both the Isc (by 31% at 10(-5) M) and the stroma-to-tear unidirectional Cl- flux. UK hyperpolarized the apical membrane potential difference and increased the transepithelial resistance and apical-to-basolateral resistance ratio. UK reduced forskolin-stimulated adenylate cyclase activity by 36%. The electrophysiological effects of UK are consistent with a reduction of the Cl- permeability at the apical membrane. Pretreatment with UK sensitized the tissue for a greater effect by forskolin. Results show that the frog corneal epithelium also possesses alpha 1- and alpha 2-receptors, the latter negatively coupled to the adenylate cyclase system. Cl- transport is thus regulated by an interaction between the positive effects of beta- and alpha 1-stimulation and the negative influence of alpha 2-stimulation.

Apical adenosine activates an amiloride-sensitive conductance in human intestinal cell line HT29cl.19A

1997 ◽  
Vol 272 (3) ◽  
pp. C931-C936 ◽  
Author(s):  
H. Bouritius ◽  
J. A. Groot
Keyword(s):  
Adenosine Receptor ◽  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Membrane Resistance ◽  
Intestinal Cell ◽  
Cation Conductance ◽  
Intestinal Cell Line ◽  
Stimulation Of

We studied the effects of stimulation of the apical adenosine receptor on ion transport by HT29cl.19A cells with the conventional microelectrode technique. Adenosine (100 microM) caused an increase in the transepithelial potential (3.6 +/- 0.4 mV) and equivalent short-circuit current (I(sc), 21 +/- 3 microA/cm2), a transient depolarization of the apical membrane potential (14 +/- 2 mV), and a decrease in the apical membrane resistance. The increase in I(sc) was additive to the effect of forskolin or basolateral addition of a maximal concentration of adenosine. Bumetanide, applied after adenosine, caused a further depolarization (7 +/- 2 mV) concomitant with a decrease in I(sc) (-13 +/- 2 microA/cm2) and an increase in the basolateral membrane resistance. Substitution of Cl- with gluconate or Na+ with N-methylglucamine reduced the response to adenosine by >60%. The response was also reduced by a low concentration of amiloride. We conclude that stimulation of the apical adenosine receptor activated a cation conductance in the apical membrane.

L-glutamine with D-glucose stimulates oxidative metabolism and NaCl absorption in piglet jejunum

1992 ◽  
Vol 263 (6) ◽  
pp. G960-G966 ◽  
Author(s):  
J. M. Rhoads ◽  
E. O. Keku ◽  
J. P. Woodard ◽  
S. I. Bangdiwala ◽  
J. G. Lecce ◽  
...  
Keyword(s):  
Oxidative Metabolism ◽  
Carbonic Acid ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Glutamine Metabolism ◽  
Nacl Absorption ◽  
The Relationship ◽  
Stimulation Of

To explore the relationship between intestinal fluid absorption and oxidative metabolism, we measured the effects of amino acids and glucose on piglet jejunal ion transport and oxygen consumption (QO2) in vitro. Jejunal QO2 was stimulated by L-glutamine and D-glucose but not by the nonmetabolizable organic solutes methyl beta-D-glucoside or L-phenylalanine. QO2 was maximally enhanced by the combination of D-glucose and L-glutamine (5 mM). Even though 5 mM L-glutamine was previously found to be insufficient to stimulate NaCl absorption, 5 mM L-glutamine enhanced jejunal NaCl flux when combined with equimolar mucosal D-glucose. Either D-glucose or methyl beta-D-glucoside caused an increase in short-circuit current (Isc), an increase in Na+ absorption in excess of Isc, and a decrease in Cl- secretion, when L-glutamine was substituted for D-glucose (10 mM) on the serosal side. This relationship suggests that mucosal sugars, if combined with L-glutamine, enhance neutral NaCl absorption as well as electrogenic Na+ flow. (Aminooxy)acetate, an inhibitor of alanine aminotransferase, abolished the stimulation of QO2 and the NaCl-absorptive response to L-glutamine. We conclude that the oxidative metabolism fueled by L-glutamine is linked to a NaCl-absorptive mechanism in the intestine. We propose that the CO2 produced by glutamine metabolism yields carbonic acid, which dissociates to H+ and HCO3-, which may stimulate parallel antiports in the apical membrane.

Effects of oxytocin on cation content and electrophysiology of frog skin epithelium

1988 ◽  
Vol 255 (3) ◽  
pp. C357-C367 ◽  
Author(s):  
H. F. Schoen ◽  
A. Kaufman ◽  
D. Erlij
Keyword(s):  
Frog Skin ◽  
Rana Catesbeiana ◽  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Flame Photometry ◽  
Intracellular Na Activity ◽  
Current Voltage

We measured effects of oxytocin on current-voltage (I-V) relations of frog (Rana catesbeiana) skins impaled with an intracellular microelectrode. In both Cl- and Cl(-)-free (SO4(2-) solutions, oxytocin caused an approximate doubling short-circuit current (Isc) and a depolarization of the cell membrane. Increase in apical membrane slope conductance, chord conductance, and permeability after oxytocin correlated with the increase in amiloride-sensitive Isc. Oxytocin also increased basolateral membrane conductance (gb). In Cl-, the shift in the voltage intercept of the apical membrane I-V relation (Ea) implied increased intracellular Na+ activity (a(Na)c) after oxytocin. In isolated frog skin epithelia, a similar increase in intracellular [Na+] after oxytocin was demonstrated by flame photometry. In SO4(2-), changes caused by oxytocin in both Ea and in flame photometrically determined cell [Na+] were minimal. The voltage intercept of the basolateral membrane I-V relations (Eb) was shifted by oxytocin in both Cl- and SO4(2-) solutions. Assuming that the basolateral membrane is selectively permeable to K+, changes in K+ obtained from Eb were in disagreement with those obtained by flame photometry. These results suggest that 1) the increase in a(Na)c caused by oxytocin is not essential to produce either the increase in gb or Isc and 2) ions other than K+ make an important contribution to basolateral membrane conductance.

β-Adrenoceptor-mediated control of apical membrane conductive properties in fetal distal lung epithelia

2002 ◽  
Vol 282 (4) ◽  
pp. L621-L630 ◽  
Author(s):  
A. Collett ◽  
S. J. Ramminger ◽  
R. E. Olver ◽  
S. M. Wilson
Keyword(s):  
Apical Membrane ◽  
Short Circuit ◽  
Anion Channel ◽  
Short Circuit Current ◽  
Lung Epithelial Cells ◽  
Disulfonic Acid ◽  
Intact Cells ◽  
Permeabilized Cells ◽  
Distal Lung ◽  
Stimulation Of

Distal lung epithelial cells isolated from fetal rats were cultured (48 h) on permeable supports so that transepithelial ion transport could be quantified electrometrically. Unstimulated cells generated a short-circuit current ( I sc) that was inhibited (∼80%) by apical amiloride. The current is thus due, predominantly, to the absorption of Na+ from the apical solution. Isoprenaline increased the amiloride-sensitive I sc about twofold. Experiments in which apical membrane Na+ currents were monitored in basolaterally permeabilized cells showed that this was accompanied by a rise in apical Na+ conductance ( G Na+ ). Isoprenaline also increased apical Cl− conductance ( G Cl− ) by activating an anion channel species sensitive to glibenclamide but unaffected by 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS). The isoprenaline-evoked changes in G Na+ and G Cl− could account for the changes in I sc observed in intact cells. Glibenclamide had no effect upon the isoprenaline-evoked stimulation of I sc or G Na+ demonstrating that the rise in G Cl− is not essential to the stimulation of Na+ transport.

Stimulation by cGMP of apical Na channels and cation channels in toad urinary bladder

1991 ◽  
Vol 260 (2) ◽  
pp. C234-C241 ◽  
Author(s):  
S. Das ◽  
M. Garepapaghi ◽  
L. G. Palmer
Keyword(s):  
Urinary Bladder ◽  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Toad Urinary Bladder ◽  
Na Channels ◽  
Serosal Side ◽  
Cyclic Monophosphate ◽  
Stimulation Of

The effects of 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) on apical membrane cation conductances in the toad urinary bladder were investigated. 8-BrcGMP (1 mM) added to the serosal solution increased the amiloride-sensitive short-circuit current (INa) after a delay of 5 min to a steady-state value 1.8 times that of controls achieved after 30 min. Similar effects were seen when the bladders were bathed on the serosal side with a normal NaCl Ringer solution and with a high-K sucrose solution to depolarize the basolateral membrane. Under the latter conditions, the amiloride-sensitive transepithelial conductance increased in parallel with the short-circuit current, indicating stimulation of apical membrane Na channels. The threshold concentration for observing the stimulation of INa was 100 microM, 10-100 times larger than the concentration of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) required to elicit an increase in INa. Currents through an outwardly rectifying Ca-sensitive cation conductance (Iout) were also increased by 1.8-fold relative to controls. This stimulatory effect occurred after a delay of 15 min and reached maximal levels 90-120 min after addition of the nucleotide. The effects of cGMP on INa were not additive with those of 8-BrcAMP or with antidiuretic hormone, an agent known to act by increasing cAMP within the cell. Addition of 1 mM 3-isobutyl-1-methylxanthine to the serosal side of the bladders stimulated INa by 1.3-fold and Iout by 2.4-fold. In both cases, subsequent addition of cGMP produced no further activation of either conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

The concentration-dependence of CRF-like diuretic peptide: mechanisms of action.

1998 ◽  
Vol 201 (11) ◽  
pp. 1753-1762 ◽  
Author(s):  
T M Clark ◽  
T K Hayes ◽  
G M Holman ◽  
K W Beyenbach
Keyword(s):  
Short Circuit ◽  
Second Messenger ◽  
Short Circuit Current ◽  
Paracellular Pathway ◽  
Ionophore A23187 ◽  
Na Transport ◽  
Principal Mechanism ◽  
Cl Transport ◽  
Mediated Effects ◽  
Stimulation Of

The mechanism of action of synthetic CCRF-DP, the corticotropin-releasing factor (CRF)-related diuretic peptide of the salt marsh mosquito Culex salinarius, was investigated in isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti. A low concentration of CCRF-DP (10(-9)mol l-1) caused a small but insignificant increase in transepithelial secretion of NaCl and fluid, but significantly reduced transepithelial voltage and resistance without a change in short-circuit current, pointing to the stimulation of passive Cl- transport through the paracellular pathway as the principal mechanism of a mild diuresis. Significant changes in voltage and resistance but not in short-circuit current were duplicated by the ionophore A23187 (0.4 micromol l-1), suggesting Ca2+ as a second messenger at 10(-9)mol l-1 CCRF-DP. A high concentration of CCRF-DP (10(-7)mol l-1) significantly increased transepithelial secretion of NaCl and fluid and significantly increased short-circuit current, pointing to the stimulation of active Na+ transport through the transcellular pathway as the mechanism of a strong diuresis. This effect was mimicked by dibutyryl-cAMP, suggesting cAMP as a second messenger at 10(-7)mol l-1 CCRF-DP. Dibutyryl-cGMP had no effects. These results suggest dose-dependent, receptor-mediated effects of CCRF-DP that target discrete transport pathways via discrete second messengers: low concentrations of CCRF-DP cause a mild diuresis, apparently via Ca2+-mediated effects on paracellular Cl- transport, and high concentrations cause a strong diuresis via cAMP-mediated effects on active transcellular Na+ transport in addition to the effects on the paracellular pathway.

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