Differentiation of two distinct K conductances in the basolateral membrane of turtle colon.

1. The whole-cell and single channel patch clamp techniques were used to identify K+-selective conductances in single proximal tubule cells isolated from frog kidney and to examine their ATP sensitivity. Whole-cell currents were inhibited by the K+ channel inhibitors Ba2P and quinidine in a dose-dependent manner. Addition of Ba2+ alone, quinidine alone, or both inhibitors together revealed two separate conductances, one of which was blocked by both Ba2P and quinidine (GBa), the other being sensitive to quinidine alone (Gquin).2. With Na+-containing Ringer solution in the bath and K+-containing Ringer solution in the pipette, both currents were selective for K+ over Nae. The K+: Na+ selectivity ratio of GBa was around 50: 1, while that of Gquin was 4: 1. In symmetrical KCl solutions GBa showed inward rectification, while Gquin demonstrated outward rectification. 3. In the absence of pipette ATP, both GBa and Gquin ran down over 10 min. However, when 2 mm ATP was included in the pipette GBa increased, while Gquin remained unchanged. 4. Single channel studies demonstrated that a basolateral K+ channel shared several of the characteristics of GBa. It was inhibited by both Ba2P and quinidine, underwent run-down in excised patches in the absence of ATP, and was activated by ATP.

Section: Single Channel Currentsmentioning

confidence: 67%

Two K(+)‐selective conductances in single proximal tubule cells isolated from frog kidney are regulated by ATP.

Robson

Hunter

1997

“…The sudden appearance of these channels in inside-out patches immediately after patch excision into a Ca2+-containing medium was the first indication that the Quinidine and lidocaine were also tested on the inward-rectifying K+ channel as these agents selectively block one type of macroscopic K+ conductance in the turtle colon (Germann, Ernst & Dawson, 1986 a;Germann, Lowy, Ernst & Dawson, 1986b) and also block the single channels thought to be responsible for that conductance (Richards & Dawson, 1986). As shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Selective block of specific K(+)‐conducting channels by diphenylamine‐2‐carboxylate in turtle colon epithelial cells.

Richards

Dawson

1993

Self Cite

SUMMARY1. The conduction and gating properties of K+-conducting channels were studied in isolated turtle colon cells in an attempt to identify the single channels responsible for specific components of the macroscopic conductance of the basolateral membrane. Three types of Ca2+-activated channel were identified, two of which were selective for K+ over Na+ and a third which was selective for monovalent cations over anions, but did not discriminate between K+ and Na+.2. One of the K+-selective channels was a large-conductance 'maxi' K+ channel. A second was characterized by a lower conductance and pronounced inward rectification.3. The inward-rectifying K+ channel was selectively blocked by diphenylamine-2-carboxylate (DPC). Neither the maxi K+ channel nor a previously identified K+-selective channel thought to be activated by cell swelling was affected by this compound. DPC also blocked the non-selective cation channel.4. An inward-rectifying, DPC-sensitive current was prominent in whole cellrecordings, and DPC blocked basolateral K+ currents in colonic cell layers apically permeabilized with amphotericin-B. In addition, the compound blocked active Na+ absorption.5. The selective block of a class of epithelial K+ channels by DPC may be a useful tool for determining the contribution of this specific subpopulation to macroscopic conductance and transepithelial salt transport.

“…One population of basolateral K+ channels appears to mediate the recycling of K+ necessary to maintain electrogenic Na+ absorption (Germann, Ernst & Dawson, 1986a) and is blocked by DPC (Richards & Dawson, 1989) but not by serosal TEA+ up to 20 mM (Germann et al 1986b). Another distinct population appears to mediate swellinginduced basolateral K+ exit (Germann et al 1986a) and is blocked by quinidine and lidocaine (Richards & Dawson, 1986) but not by up to 20 mm TEA' (Germann et al 1986b). Blockade of these channels by lidocaine also induces current fluctuations that produce a Lorentzian component in the PDS (Dawson, Van Driessche & Helman, 1988).…”

Section: Tea+-sensitive Apical K+ Channels Mediate Active K+ Secretionmentioning

confidence: 99%

“…Those results suggested that K+ exited the epithelial cells via a population of K+-permeable channels in the apical membrane, although the mechanism for inhibition by amiloride was not clear. Turtle colon is also well suited for a comparison between apical and basolateral K+ channels because several populations of basolateral K+ channels have been identified and can be distinguished by blocker specificity (Germann, Lowy, Ernst & Dawson, 1986b;Chang & Dawson, 1988;Richards & Dawson, 1989).…”

Section: Introductionmentioning

confidence: 99%

Tetraethylammonium‐sensitive apical K+ channels mediating K+ secretion by turtle colon.

Wilkinson

Kushman

Dawson

1993

Self Cite

SUMMARY1. Apical membrane K+ channels in turtle colon were identified and characterized using current fluctuation analysis.2. Under short-circuit conditions in NaCl-Ringer solution, the power density spectrum (PDS) of the short-circuit current (I.C) sometimes exhibited a clearly discernible Lorentzian component, indicating spontaneous fluctuations produced by a population of apical ion channels. The Lorentzian component had a characteristic corner frequency (fe) which averaged 10-2+0-9 Hz (mean+s.E.M., n = 20). -50-115 mm, Na+ replacement), by clamping the transepithelial potential (Vt) to serosa-positive values, or by blocking basolateral K+ channels with Ba2+. 4. Mucosal amiloride (100 ,UM) attenuated the spontaneous fluctuations observed in NaCl-Ringer solution but had no effect in the presence of serosal high K+, indicating that amiloride did not block the K+-permeable channels but these channels resided in the same cells as the amiloride-sensitive Na+ channels.5. Raising the mucosal K+ concentration attenuated spontaneous fluctuations. 6. In the presence of serosal high K+ and mucosal amiloride, the spontaneous fluctuations were often accompanied by a reversed ISC consistent with K+ secretion. These conditions were used to test the effects of putative channel blockers.7. Mucosal Ba2+ and tetraethylammonium (TEA+) were effective inhibitors of the spontaneous fluctuations and the reversed ISC. At a concentration of 10 mm, TEA+ was maximally effective but the TEA+ analogues tetramethylammonium (TMA+) and tetrapropylammonium (TPrA+) were much less effective. Mucosal Rb+ or Cs+ did not inhibit at a concentration of 10 mm. 10. These experiments identified a population of TEA'-sensitive, apical K+ channels which mediate active K+ secretion in turtle colon. Sensitivity to external TEA+ distinguishes these channels from basolateral K+ channels in turtle colon and demonstrates similarity to apical K+ channels in mammalian colon.