Hypertonic cell volume regulation in mouse thick limbs. I. ADH dependency and nephron heterogeneity

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Abstract
Differential interference contrast microscopy was used in combination with standard electrophysiological techniques in the in vitro perfused mouse medullary (mTALH) and cortical (cTALH) thick ascending limbs of Henle to evaluate the cell volume responses of these nephron segments to sudden increases in peritubular osmolality and to assess the role of antidiuretic hormone (ADH) and net NaCl absorption on hypertonic volume regulation. In the absence of CO2/HCO3- in external media, the cells of the mTALH behaved in a simple osmometric fashion, with an osmotic space equivalent to 70-80% of the total cell volume. However, in CO2/HCO3- -containing media, the cells of the mTALH, but not the cTALH, were able to increase their cell volume to the original volume after shrinkage in peritubular media made hypertonic with either NaCl or mannitol. This volume-regulatory increase response (VRI) in the mTALH was mediated by an increase in intracellular osmoles, and required peritubular ADH, at concentrations that stimulate maximally the rate of net NaCl absorption. This ADH effect on VRI could be mimicked by addition of dibutyryladenosine 3',5'-cyclic monophosphate to the bath in the absence of hormone. However, 10(-4) M luminal furosemide, a concentration that abolishes ADH-dependent NaCl absorption in the mTALH, had no effect on the VRI response. These results indicate that the cells of the mTALH, but not the cTALH, are capable of hypertonic volume regulation, that ADH (via adenosine 3',5'-cyclic monophosphate) is required for expression of the VRI response in the mTALH, and that the effects of ADH on net NaCl absorption and the VRI response in the mTALH are completely dissociable. Thus these results are consistent with a role for ADH in hypertonic VRI in the mammalian mTALH, which may operate to maintain constant cell volume in this nephron segment during antidiuresis.

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