Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the cortical collecting duct of the rat two Ca(2+)-dependent K+ channels have been described so far. In the luminal membrane a maxi K+ channel with a single channel conductance of 139 +/- 3 pS in excised membrane patches (n = 91) at 0 mV clamp voltage and asymmetrical KCl-concentrations in pipette and bath was found, while in the basolateral membrane an intermediate conductance K+ channel (85 +/- 1 pS, n = 53) and a small K+ channel (28 +/- 2 pS, n = 15) was described. All these K+ channels had similar pharmacological properties since all could be blocked by the K+ channel inhibitors Ba2+, TEA+, and charybdotoxin. Verapamil, known as a L-type Ca2+ channel blocker, was also capable of inhibiting these K+ channels. While the maxi K+ channel from the luminal membrane was upregulated by intracellular Ca2+ (EC50: 5 microM), the small and the intermediate K+ channel from the basolateral membrane were downregulated (IC50: 10 microM). When the cytosolic Ca(2+)-activity was in the physiological range below 1 microM the activity of the maxi K+ channel was low and regulated via intracellular pH and ATP. Furthermore, when CCD cells were strongly depolarized and under hypoosmotic stress, Ca2+ rose and activated this K+ channel, indicating that this channel is involved in volume regulation. Like the maxi K+ channel the intermediate conductance K+ channel from the basolateral membrane was also sensitive to intracellular changes of pH where acidic pH inhibited while alkaline pH activated this channel. But unlike the K+ channels from the luminal membrane the K+ channel from the basolateral membrane is not regulated by ATP up to 5 mM. The activity of the K+ channels from the basolateral membrane decreased steadily after excision of the membrane. This decrease could be prevented by applying cGMP and MgATP to the bath and thus, activating a membrane-bound cGMP-dependent protein kinase (PKG). The activation of the PKG could be reversed by its specific inhibitor KT5823 (1 microM). Due to the opposite regulation via intracellular Ca2+ and the involvement of different protein kinases a specific and independent regulation of K+ secretion and Na+ reabsorption is possible in the CCD of the rat.
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PMID:Ca(2+)-dependent K+ channels in the cortical collecting duct of rat. 926 90

The purpose of this study was to examine cation channel activity in the apical membrane of the outer medullary collecting duct of the inner stripe (OMCD(i)) using the patch-clamp technique. In freshly isolated and lumen-opened rabbit OMCD(i), we have observed a single channel conductance of 23.3 +/- 0.6 pS (n = 17) in cell-attached (c/a) patches with high KCl in the bath and in the pipette at room temperature. Channel open probability varied among patches from 0.06 +/- 0.01 at -60 mV (n = 5) to 0.31 +/- 0.04 at 60 mV (n = 6) and consistently increased upon membrane depolarization. In inside-out (i/o) patches with symmetrical KCl solutions, the channel conductance (22.8 +/- 0.8 pS; n = 10) was similar as in the c/a configuration. Substitution of the majority of Cl- with gluconate from KCl solution in the pipette and bath did not significantly alter reversal potential (E(rev)) or the channel conductance (19.7 +/- 1.1 pS in asymmetrical potassium gluconate, n = 4; 21.4 +/- 0.5 pS in symmetrical potassium gluconate, n = 3). Experiments with 10-fold lower KCl concentration in bath solution in i/o patches shifted E(rev) to near the E(rev) of K+. The estimated permeability of K+ vs. Cl- was over 10, and the conductance was 13.4 +/- 0.1 pS (n = 3). The channel did not discriminate between K+ and Na+, as evidenced by a lack of a shift in the E(rev) with different K+ and Na+ concentration solutions in i/o patches (n = 3). The current studies demonstrate the presence of cation channels in the apical membrane of native OMCD(i) cells that could participate in K+ secretion or Na+ absorption.
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PMID:Apical membrane of native OMCD(i) cells has nonselective cation channels. 1139 45

Transition from antidiuresis to diuresis exposes cortical collecting duct cells (CCD) to asymmetrical changes in environment osmolality, inducing an osmotic stress, which activates numerous membrane-associated events. The aim of the present work was to investigate, either in the presence or not of AQP2, the transepithelial osmotic water permeability (P(osm)) following cell exposure to asymmetrical hyper- or hypotonic gradients. For this purpose, transepithelial net volume fluxes were recorded every minute in two CCD cell lines: one not expressing AQPs (WT-RCCD(1)) and another stably transfected with AQP2 (AQP2-RCCD(1)). Our results demonstrated that the rate of osmosis produced by a given hypotonic shock depends on the gradient direction (osmotic rectification) only in the presence of apical AQP2. In contrast, hypertonic shocks elicit P(osm) rectification independently of AQP2 expression, and this phenomenon may be linked to modulation of basolateral membrane permeability. No asymmetry in transepithelial resistance was observed under hypo- or hypertonicity, indicating that rectification cannot be attributed to a shunt through the tight junction path. We conclude that osmotic rectification may be explained in terms of dynamical changes in membrane permeability probably due to activation/incorporation of AQPs or transporters to the plasma membrane via some mechanism triggered by osmolality.
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PMID:Asymmetry in the osmotic response of a rat cortical collecting duct cell line: role of aquaporin-2. 1655 Apr 85