AJP - Renal Physiology, Vol 260, Issue 6 833-F838, Copyright © 1991 by American Physiological Society

ARTICLES

Mechanisms of inhibition of proximal acidification by PTH

S. Sasaki and F. Marumo
Second Department of Internal Medicine, Tokyo Medical and Dental University, Japan.

The parathyroid hormone (PTH) effects on luminal Na-H exchange and basolateral Na-HCO3 cotransport were examined in isolated perfused rabbit proximal convoluted tubules. Lumen pH (pHi) and cell pH (pHi) were measured by a fluorescent technique using 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF). The time course of the PTH effect on proximal acidification was first determined by continuous monitoring of pHi in a stop-flow condition. PTH 10(-8) M added to the bath promptly inhibited the acid pHl generation. Adenosine 3',5'-cyclic monophosphate (cAMP) (10(-4) M) added to the bath mimicked the PTH effect. Luminal Na-H exchange was assayed by monitoring changes in pHi (dpHi/dt) in response to luminal Na+ removal in HCO3- free condition. The addition of PTH or cAMP for 5 min decreased dpHi/dt by 30 and 37%, respectively. Basolateral Na-HCO3 cotransport was assayed by measuring dpHi/dt caused by bath Na+ removal. The addition of PTH or cAMP for 5 min did not change the dpHi/dt. PTH also did not alter the dpHi/dt induced by reducing the bath HCO3- from 25 to 5 mM. The addition of PTH or cAMP to the bath slightly reduced pHi by 0.05. These results suggest that 1) PTH inhibits proximal acidification very rapidly and the effect reached a maximum within 10 min, 2) PTH rapidly inhibits luminal Na-H exchange but not basolateral Na-HCO3 cotransport in a short period, and 3) this effect is at least partly mediated by cAMP-dependent mechanisms.

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