Interrelationship between cell pH and cell calcium in rat inner medullary collecting duct cells

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Abstract
In this study we investigated the interrelationship between cell pH (pHi) and cell calcium (Cai) in cultured inner medullary collecting duct cells of the rat. Confluent monolayers were made quiescent by incubation for 24 h in Dulbecco's modified Eagle's medium supplemented with 0.1% serum before study. Changes in pHi and Cai were measured with the fluorescent probes 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein and fura 2. In nominally bicarbonate-free media containing 110 mM Na+ and 1 mM Cai, cell acidification to pH 6.70 increased Cai from 122 +/- 24 to 243 +/- 33 nM. In the absence of bath calcium, acidification increased Cai from 90 +/- 7 to 144 +/- 13 nM. An increase of pHi to 7.6 reduced Cai almost to baseline. Cell acidification increased inositol trisphosphate (IP3) production, and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester, an IP3 antagonist, partially inhibited the rise in Cai. Elevation of Cai resulted in a sustained cell alkalinization from 7.32 +/- 0.02 to 7.58 +/- 0.04. When Cai was reduced, pHi fell to 7.25 +/- 0.01. We conclude that Cai and pHi participate in a feedback loop that modulates changes in each respective parameter.