Na(+)-Ca2+ exchange and Ca2+ depletion in rat proximal tubules.
The removal of external Ca2+ ([Ca2+]o) reduces cytosolic Ca2+ ([Ca2+]i) in rat proximal tubules. In this report the role of external Na+ ([Na+]o) on the changes of [Ca2+]i and Ca2+ efflux caused by withdrawal of [Ca2+]o is described in rat renal proximal tubules. In aequorin-loaded tubules [Ca2+]i decreased from 235 +/- 25 to 48 +/- 16 (n = 4, P = 0.017), and 45Ca2+ fractional efflux ratio (45Ca2+ FER) increased from 0.94 +/- 0.03 to 1.64 +/- 0.19 (n = 6, P = 0.021) when Ca2+ was withdrawn from the bathing media of Krebs buffer (KB). The fall of [Ca2+]i, as well as the activation of 45Ca2+ FER, was reversed when [Na+]o in Ca(2+)-free KB was lowered isosmotically from 150 to 15 mM. However, when tubules were superfused with only 5 mM [Na+]o before [Ca2+]o was removed, [Ca2+]i also declined, but 45Ca2+ FER did not increase. The Na(+)-Ca2+ exchange inhibitor dichlorobenzamil (DCB) added after [Ca2+]o was removed evoked responses similar to [Na+]o removal, although DCB also inhibited internal Ca2+ release. These results are congruous with stimulation of Na+ influx in exchange for [Ca2+]i in Ca(2+)-free KB. However, even though total tubular Na+ was higher in Ca(2+)-free KB after 10 min, the initial rate of 22Na+ influx was not different without or with [Ca2+]o.(ABSTRACT TRUNCATED AT 250 WORDS)
Dominguez
J H
JH
Nephrology Section, Veterans Administration Medical Center, Indianapolis, Indiana 46223.
Mann
C
C
Rothrock
J K
JK
Bhati
V
V
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D051381:Rats; D012964:Sodium / Q000493:pharmacokinetics; D019831:Sodium-Calcium Exchanger; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; C041470:3',4'-dichlorobenzamil; D000584:Amiloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium