Parathyroid hormone inhibition of Na+-H+ antiporter activity in a cultured renal cell line.
The renal effects of parathyroid hormone (PTH) include a decreased rate of acidification by the proximal tubule. To determine whether this effect represented a PTH action on the Na+-H+ antiporter, we investigated the effect of PTH on the established opossum kidney (OK) cell line. This cell line retains several features characteristic of proximal tubule cells, including an amiloride-sensitive Na+-H+ antiporter and high-affinity PTH receptors with a coupled cAMP response. We measured steady-state intracellular pH and amiloride-sensitive 22Na+ uptake as a reflection of the activity of the Na+-H+ antiporter. Under bicarbonate and CO2-free conditions, the steady-state intracellular pH of OK cell cultures was modified by altering the rate of Na+-H+ exchange. When Na+-H+ exchange was inhibited by amiloride, intracellular pH fell. Conversely, augmenting antiporter activity by addition of monensin, a Na+-H+ exchange ionophore, raised intracellular pH. PTH (2.5 X 10(-8) M) lowered intracellular pH by up to 0.17 pH units, and half of the maximum PTH effect was present at a concentration of 10(-12) M. This effect was not seen in the presence of amiloride or in the absence of sodium, suggesting that a functional Na+-H+ antiporter is necessary for its expression. The decrease in intracellular pH was reproduced by forskolin and 8-bromo-cAMP, suggesting that this is a cAMP-mediated effect. PTH, forskolin, and 8-bromo-cAMP also decreased the amiloride-sensitive component of 22Na+ uptake in OK cells by up to 64%, whereas the amiloride-insensitive component was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)
Pollock
A S
AS
Warnock
D G
DG
Strewler
G J
GJ
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors*; D002460:Cell Line; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D006601:Hexoses / Q000032:analysis; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology; D009893:Opossums; D010042:Ouabain / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D010281:Parathyroid Hormone / Q000494:pharmacology*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D006601:Hexoses; D010281:Parathyroid Hormone; D017923:Sodium-Hydrogen Exchangers; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D010042:Ouabain; D000584:Amiloride; D008985:Monensin; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine