Submitted on August 6, 2002
Accepted on December 15, 2002
Parathyroid Hormone Stimulates a Chloride-Dependent and EIPA-Sensitive Current in Chick Proximal Tubule Cells in Culture
Gary Laverty1*, Colleen McWilliams1, Amanda Sheldon1, and Sighvatur S. Arnason2
1 Department of Biological Sciences, University of Delaware, Newark, DE, USA
2 Department of Physiology, University of Iceland, Reykjavik, IS-101, Iceland
* To whom correspondence should be addressed. E-mail: laverty{at}udel.edu.
The electrophysiological effects of parathyroid hormone (PTH) were studied in a primary cell culture model of the chick (Gallus domesticus) proximal tubule. In this model confluent monolayers are grown on permeable filters and exhibit vectorial transport, including glucose-stimulated current. Under short-circuit conditions, PTH, at 10-9 M, induced a positive current (ISC) response, with an average 2 minute peak response of 14.30 ±1.58 µA/cm2 over the baseline ISC, followed by a slow decay. The PTH response was dose dependent, with a half-maximal response at 5 x 10-9 M and maximum response at 5 x 10-8. Forskolin and dibutyryl-cAMP also stimulated ISC, as did the phosphodiesterase inhibitor IBMX. In contrast, the phorbol ester PMA inhibited baseline ISC. The PTH response was nearly abolished by apical addition of 100 µM EIPA, an inhibitor of Na+/H+ exchangers, and partially blocked by the Cl- channel blockers NPPB (100 µM) and glibenclamide (300 µM). Higher doses of EIPA or NPPB alone (500 µM) were almost fully effective, with no or slight additional effects of NPPB or EIPA, respectively. The anion exchange inhibitor DIDS (100 µM) and the Na+ channel blocker amiloride (10 µM) had no effect. Bilateral reduction of chloride in the buffer, from 137 to 2.6 mM abolished the PTH response; increasing [Cl-] restored the ISC response, with a half maximal effect at 50 mM. These data suggest that in the chick proximal tubule PTH activates both a Na+/H+ exchanger and a Cl- ion channel that may be functionally linked.
