ISSN:
1432-1424
Keywords:
frog kidney
;
proximal tubule
;
HCO 3 − transport
;
K+ conductance
;
Cl− conductance
;
fusion
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Proximal tubular cells of the frog (Rana esculenta) kidney were fused within an isolated tubule portion to giant cells according to the polyethylene-glycol fusion method. Cell membrane potentials (V m ) were measured while cells were superfused with varioús experimental solutions. Rapid concentration stepchanges of different ions allowed to calculate the respective transference numbers (t ion). In some experiments the specific cell membrane resistances (R m ) were evaluated by measuringV m induced by short current pulses injected into the cell with a second electrode. The experiments reveal: i) Fused cells of the proximal tubule exhibit aV m of −49.5±1.6 mV (n=65). ii) Addition of glucose to the perfusate yields a transient depolarization, consistent with a rheogenic Na/glucose cotransport system. iii) In absence of organic substrates the whole cell membrane conductance is made up of K+ and HCO3, iv) There is a positive relationship betweenV m andtK+ and a negative relationship betweenV m andtHCO 3 − . v) HCO 3 − -inducedV m changes are attenuated or abolished when Na+ is replaced with choline+, consistent with a rheogenic Na+/HCO 3 − cotransport system. vi) Replacement of Na+ by choline+ depolarizesV m and increasesR m by about 50%; addition of 3 mmol/liter Ba2+ to the Na+-free perfusate increasesR m by about 58% compared to the initial control value. vii) There is no measurable cell membrane Cl− conductance. We conclude that fused cells of proximal tubule exert both luminal and peritubular membrane properties. In absence of organic substrates the cell membrane potential is determined by the HCO 3 − and K+ transport systems.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02209139
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