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W B Guggino

Publications and source records attributed to W B Guggino.

138 records · Page 8Linked to original sources
PubMed1985

Forskolin and antidiuretic hormone stimulate a Ca2+-activated K+ channel in cultured kidney cells.

Single channels in the apical cell membrane of primary cultured chick kidney cells were studied using the patch clamp technique. Cell-attached recordings revealed the presence of a 107 +/- 6 pS channel that increased fractional open time upon depolarization. Experiments with inside-out excised patches indicated that the channel is K+ selective, Ca2+ activated, and inhibited by Ba2+. The addition of forskolin or antidiuretic hormone (ADH) to the bath during cell-attached recordings caused an increase in the fractional open time of the channel. The activation of a K+ channel by increases in cAMP may be one way in which K+ secretion in the kidney is stimulated by ADH in vivo.

Animals↗
PubMed1984

Electrical effects of potassium and bicarbonate on proximal tubule cells of Necturus.

The effects of stepwise concentration changes of K+ and HCO3- in the basolateral solution on the basolateral membrane potential (Vbl) of proximal tubule cells of the doubly-perfused Necturus kidney were examined using conventional microelectrodes. Apparent transference numbers were calculated from changes in Vb1 after alterations in external K+ concentration from 1.0 to 2.5 mM (tK, 1.0-2.5), 2.5 to 10, and in external HCO3- concentration (at constant pH) from 5 to 10 mM (tHCO3, 5-10), 10 to 20, or 10 to 50. tK, 2.5-10 was 0.38 +/- 0.02 under control conditions but was sharply reduced to 0.08 +/- 0.03 (P greater than 0.001) by 4 mM Ba++. This concentration of Ba++ reduced Vb1 by 9 +/- 1 mV (at 2.5 external K+). Perfusion with SITS (5 X 10(-4)M) for 1 hr hyperpolarized Vb1 by 10 +/- 3 mV and increased tK, 2.5-10 significantly to 0.52 +/- 0.01 (P less than 0.001). Ba++ application in the presence of SITS depolarized Vb1 by 22 +/- 3 mV. In control conditions tHCO3, 10-50 was 0.63 +/- 0.05 and was increased to 0.89 +/- 0.07 (P less than 0.01) by Ba++ but was decreased to 0.14 +/- 0.02 (P less than 0.001) by SITS. In the absence of apical and basolateral chloride, the response of Vb1 to bicarbonate was diminished but still present (tHO3, 10-20 was 0.35 +/- 0.03). Intracellular pH, measured with liquid ion-exchange microelectrodes, increased from 7.42 +/- 0.19 to 7.57 +/- 0.17 (P less than 0.02) when basolateral bicarbonate was increased from 10 to 20 mM at constant pH. These data show that the effects of bicarbonate on Vb1 are largely independent of effects on the K+ conductance and that there is a significant current-carrying bicarbonate pathway in the basolateral membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1984

Regulation of the basolateral potassium conductance of the Necturus proximal tubule.

Two methods, the measurement of the response of the basolateral membrane potential (Vbl) of proximal tubule cells of Necturus to step changes in basolateral K+ concentration, and cellular cable analysis, were used to assess the changes in basolateral potassium conductance (GK) caused by a variety of maneuvers. The effects of some of these maneuvers on intracellular K+ activity (aiK) were also evaluated using double-barreled ion-selective electrodes. Perfusion with 0 mM K+ basolateral solution for 15 min followed by 45 min of 1 mM K+ solution resulted in a fall in basolateral potassium (apparent) transference number (tK), Vbl and aiK. Results of cable analysis showed that total basolateral resistance, Rb, rose. The electrophysiological effects of additional manipulations, known to inhibit net sodium reabsorption across the proximal tubular epithelium of Necturus, were also investigated. Ouabain caused a fall in tK accompanied by large decreases in aiK and Vbl. Lowering luminal sodium caused a fall in tK and a small reduction in Vbl. Selective reduction of peritubular sodium, a maneuver that has been shown to block sodium transport from lumen to peritubular fluid, also resulted in a significant decrease in tK. These results suggest that GK varies directly with rate of transport of the sodium pump, irrespective of the mechanism of change in pump turnover.

Animals↗
PubMed1983

Regulation of intracellular chloride activity during perfusion with hypertonic solutions in the Necturus proximal tubule.

In a previous study we presented evidence that chloride transport across the basolateral membrane in Necturus proximal tubule cells occurs predominantly via exchange for both Na+ and HCO3-. In this study the regulation of intracellular chloride was further examined in the doubly-perfused kidney preparation using conventional and chloride-sensitive microelectrodes. Application of hypertonic basolateral solutions containing 80 mM raffinose stimulated an efflux of chloride such that chloride activity remained unchanged at control levels. Membrane potential did not change in these experiments. Inhibition of Cl- exit across the basolateral cell membrane by removal of either HCO3- or Na+ from the perfusion solution resulted in a significant increase in intracellular chloride activity, aiCl, when basolateral osmolarity was raised. Hypertonic basolateral solutions also produced a significant rise in aiCl in the presence of SITS. This study provides further evidence that chloride is transported across the basolateral cell membrane in exchange for both Na+ and HCO3-. Since this exchange mechanism is activated in response to hypertonic solutions, these studies suggest a functional role for this exchanger in the regulation of aiCl in the Necturus proximal tubule cell during volume changes.

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PubMed1983

Chloride transport across the basolateral cell membrane of the Necturus proximal tubule: dependence on bicarbonate and sodium.

The transport of chloride across the Necturus proximal tubule cell was studied in the doubly-perfused kidney using conventional, chloride-sensitive and pH-sensitive microelectrodes. Lowering chloride activity in the basolateral solution results in a reduction in intracellular Cl- activity (aiCl). This reduction in aiCl is inhibited by removing either HCO-3 or Na+ from the perfusion solution, indicating that both HCO-3 and Na+ are required for Cl- movement across the basolateral cell membrane. Reducing either HCO-3 or Na+ in the basolateral solution causes an increase in aiCl. Thus changes in either Na+ or HCO-3 chemical gradients across the basolateral cell membrane significantly affect chloride movement. Changing intracellular pH by means of NH4Cl exposure results in an increase in aiCl followed by a sharp decrease when NH4Cl is removed. These changes in intracellular chloride do not occur in the absence of HCO-3. Likewise, the decrease in aiCl following NH4Cl treatment requires the presence of Na+ in the basolateral solution. We conclude that chloride is transported across the basolateral cell membrane in exchange for both Na+ and HCO-3. Our results also support the presence of a Na+/Cl- cotransport mechanism on the apical cell membrane.

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PubMed1982

Cellular and paracellular resistances of the Necturus proximal tubule.

Individual resistances of the apical cell membrane Ra, the basolateral cell membrane, Rbl, and the paracellular shunt, Rs, were determined in the Necturus proximal tubule using a set of three electrical parameters. Four electrical parameters were measured: the transepithelial resistance, (Rte), the apical and basolateral cell membrane resistance in parallel, (Rz free-flow tubules), the basolateral cell membrane resistance in oil-filled tubules, (Rz oil-filled), and the ratio of apical and basolateral cell membrane resistance (Ra/Rbl). Rte was determined from an analysis of the spatial decay of luminal voltage following luminal current injection. Rz free-flow and Rz oil-filled were measured by the analysis of the spatial decay of intracellular voltage deflections following cellular current injection in free flow and oil-filled tubules, respectively. Ra/Rbl was estimated from the ratio of voltage deflections across the apical and basolateral cell membranes following transepithelial current injection. In addition, the magnitude of cellular and luminal cable interactions was evaluated, by comparing the spatial decay of voltage deflections in the cell and in the lumen following intracellular current injection. The combined cell membrane resistance (Ra + Rbl) is between one to two orders of magnitude greater than the paracellular resistance. This result supports the view that the Necturus proximal tubule is a leaky epithelium.

Animals↗
PubMed1982

Electrical properties of chloride transport across the necturus proximal tubule.

The chloride conductance of the basolateral cell membrane of the Necturus proximal tubule was studied using conventional and chloride-sensitive liquid ion exchange microelectrodes. Individual apical and basolateral cell membrane and shunt resistances, transepithelial and basolateral cell membrane potential differences, and electromotive forces were determined in control and after reductions in extracellular Cl-. When extracellular Cl- activity is reduced in both apical and basolateral solutions the resistance of the shunt increases about 2.8 times over control without any significant change in cell membrane resistances. This suggests a high Cl- conductance of the paracellular shunt but a low Cl- conductance of the cell membranes. Reduction of Cl- in both bathing solutions or only on the basolateral side hyperpolarizes both the basolateral cell membrane potential difference and electromotive force. Hyperpolarization of the basolateral cell membrane potential difference after low Cl- perfusion was abolished by exposure to HCO-3-free solutions and SITS treatment. In control conditions, intracellular Cl- activity was significantly higher than predicted from the equilibrium distribution across both the apical and basolateral cell membranes. Reducing Cl- in only the basolateral solution caused a decreased in intracellular Cl-. From an estimate of the net Cl- flux across the basolateral cell membrane and the electrochemical driving force, a Cl- conductance of the basolateral cell membrane was predicted and compared to measured values. It was concluded that the Cl- conductance of the basolateral cell membrane was not large enough to account for the measured flux of Cl- by electrodiffusion alone. Therefore these results suggest the presence of an electroneutral mechanism for Cl- transport across the basolateral cell membrane of the Necturus proximal tubule cell.

Animals↗
PubMed1980

Water balance in embryos of Fundulus heteroclitus and F. bermudae in seawater.

The purpose of this study is to examine the mechanisms of osmoregulation in embryos of Fundulus heteroclitus and F. bermudae. The turnover rate of tritiated water in intact embryos of F. heteroclitus increases from 0.05 to 0.013 h-1 at 4 days to 0.12 +/- 0.030 h-1 at 7 days and to 0.18 +/- 0.060 h-1 at 10 days, corresponding to estimated diffusional water permeabilities of 0.4, 1.0, and 1.6 x 10(-6) cm . s-1, respectively. These values are low when compared to other organisms but not sufficiently low to maintain embryos in water balance. The osmolality of the embryonic extracellular fluids decreases during development from 362 +/- 9.2 mosmol . kg-1 at 4 days to 344 +/- 6.9 mosmol . kg-1 at 10 days. Water loss is balanced by drinking seawater at a rate of 600 pl . mg-1 . h-1 for 7- to 8-day embryos. The embryo possesses a pair of branchial chambers that communicate anteriorly with the pharynx through embryonic gill slits and posteriorly with the perivitelline space by means of pores. In the absence of a mouth it is probably through these pores that seawater is injested.

Animals↗
PubMed1980

Salt balance in embryos of Fundulus heteroclitus and F. bermudae adapted to seawater.

22Na+ and 36Cl- tracer flux experiments of embryos of Fundulus heteroclitus show that a significant influx and efflux of Na+ and Cl- occur during development. The average influx for Na+ and Cl-, respectively, are 5.0 +/- 0.76 and 1.1 +/- 0.1 nmol . mg-1 . h-1. The average effluxes are 4.9 +/- 0.95 and 3.0 +/- 0.01 nmol . mg-1 . h-1 for Na+ and Cl-, respectively. The electrical potential across the embryonic cavity epithelium of F. heteroclitus and F. bermudae is 50 +/- 1.7 mV and 40 +/- 1.3 mV, respectively (inside positive). Diluting the artificial seawater bathing medium with distilled water decreases the potential across the embryonic cavity of F. bermudae to -11 +/- 5.0 mV at 5% artificial seawater. Because in seawater the potential across the embryonic cavity epithelium is inside positive, the efflux of Cl- is against its electrical potential gradient indicating an active extrusion mechanism for Cl-. The site of the active extrusion mechanism for chloride is located in the yolk sac where chloride cells associated with blood vessels are common.

Adaptation, Physiological↗
PubMedDate not supplied

Co-assembly of polycystin-1 and -2 produces unique cation-permeable currents.

The human kidney is composed of roughly 1.2-million renal tubules that must maintain their tubular structure to function properly. In autosomal dominant polycystic kidney disease (ADPKD) cysts develop from renal tubules and enlarge independently, in a process that ultimately causes renal failure in 50% of affected individuals. Mutations in either PKD1 or PKD2 are associated with ADPKD but the function of these genes is unknown. PKD1 is thought to encode a membrane protein, polycystin-1, involved in cell-cell or cell-matrix interactions, whereas the PKD2 gene product, polycystin-2, is thought to be a channel protein. Here we show that polycystin-1 and -2 interact to produce new calcium-permeable non-selective cation currents. Neither polycystin-1 nor -2 alone is capable of producing currents. Moreover, disease-associated mutant forms of either polycystin protein that are incapable of heterodimerization do not result in new channel activity. We also show that polycystin-2 is localized in the cell in the absence of polycystin-1, but is translocated to the plasma membrane in its presence. Thus, polycystin-1 and -2 co-assemble at the plasma membrane to produce a new channel and to regulate renal tubular morphology and function.

Animals↗