K depletion enhances the extracellular Ca2+-induced inhibition of the apical K channels in the mTAL of rat kidney.
We have shown previously that raising extracellular Ca(2)+ inhibited the apical 70-pS K channel in the thick ascending limb (TAL; Wang, W.H., M. Lu, and S.C. Hebert. 1996. Am. J. Physiol. 270:C103-C111). We now used the patch-clamp technique to study the effect of increasing the extracellular Ca(2)+ on the 70-pS K channel in the mTAL from rats on a different K diet. Increasing the extracellular Ca(2)+ from 10 microM to 0.5, 1, and to 1.5 mM in the mTAL from rats on a K-deficient (KD) diet inhibited the channel activity by 30, 65, and 90%, respectively. In contrast, raising the extracellular Ca(2)+ to 1.5 mM had no significant effect on channel activity in the mTAL from animals on a high K (HK) diet and further increasing the extracellular Ca(2)+ to 2.5, 3.5, and 5.5 mM decreased the channel activity by 29, 55, and 90%, respectively. Inhibition of the cytochrome P450 monooxygenase completely abolished the effect of the extracellular Ca(2)+ on channel activity in the mTAL from rats on a different K diet. In contrast, blocking cyclooxygenase did not significantly alter the responsiveness of the 70-pS K channel to the extracellular Ca(2)+. Moreover, addition of sodium nitropruside, a nitric oxide (NO) donor, not only increased the channel activity, but also blunted the inhibitory effect of the extracellular Ca(2)+ on the 70-pS K channel and decreased 20-hydroxyeicosatetraenoic acid (20-HETE) concentration in the mTAL from rats on a KD diet. In contrast, inhibiting NOS with L-NAME enhanced the inhibitory effect of the extracellular Ca(2)+ on the channel activity and increased 20-HETE concentration in the mTAL from rats on a high K diet. Western blot has further shown that the expression of inducible NO synthase (iNOS) is significantly higher in the renal medulla from rats on an HK diet than that on a KD diet. Also, addition of S-nitroso-N-acetylpenicillamine abolished the inhibitory effect of arachidonic acid on channel activity in the mTAL, whereas it did not block the inhibitory effect of 20-HETE. We conclude that a low dietary K intake increases the sensitivity of the 70-pS K channel to the extracellular Ca(2)+, and that a decrease in NOS activity is involved in enhancing the inhibitory effect of the extracellular Ca(2)+ on channel activity in the mTAL during K depletion.
Gu
Rui-Min
RM
Department of Pharmacology, New York Medical College, Valhalla, NY 10595, USA.
Wei
Yuan
Y
Jiang
Ho-Lin
HL
Lin
Dao-Hong
DH
Sterling
Hyacinth
H
Bloom
Peter
P
Balazy
Micheal
M
Wang
Wen-Hui
WH
D000818:Animals; D002118:Calcium / Q000502:physiology*; D018118:Chloride Channels / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000502:physiology*; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis; D052247:Nitric Oxide Synthase Type II; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D011191:Potassium Deficiency / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D018118:Chloride Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D002118:Calcium