Volume adjustment by renal medullary cells in hypo‐ and hyperosmolal solutions containing permeant and impermeant solutes.

Abstract

SUMMARY1. The changes in the volumes of cells in slices (thickness 0S3-04 mm) of rat renal outer and inner medulla have been investigated during aerobic incubation for 20 min at 370 C in Krebs phosphate-bicarbonate Ringer modified by the addition of urea or sucrose in order to produce a range of media hypo-and hyperosmolal with respect to the calculated tissue fluid osmolalities in these regions.2. On the assumption that under these conditions the measured inulin space approximates to the true extracellular space (ECS), it was found that osmotic swelling or shrinkage of cells was not accompanied by any significant variation in the absolute size of the ECS.3. Calculated cell volume changes in both regions were minimal when slices were incubated in urea-containing media iso-osmolal with tissue fluids in that region. In sucrose-containing media minimal cell volume changes occurred when media were hypo-osmolal in relation to tissue fluids by a factor of approximately 0-68.4. In all except the most hypo-osmolal media studied, calculated cell volume changes (as percentage of initial volume) were linearly related to the reciprocal of the incubation media osmolalities. The points of interception of the regression lines on the cell volume axis were dependent upon both the region studied and the composition of the incubation medium (urea or sucrose).5. These changes were accompanied by variations in slice solute concentrations. Slice [Na] was greatest, and slice [K] least, following incubation in those media producing the greatest percentage changes in cell volume.6. The volume of distribution of [14C]sucrose within the inner medulla was 61-7 + 2*5 ,ul./100 mg wet weight of tissue (mean + s.E., n = 6) after 10 min incubation. The increase to 708 + 4-2 2l./lO0 mg (n = 6) after 100 min was not significant (041 > P > 0.05). The volume of distribution within the outer medulla rose markedly during this period, from 38'1 to 582 ,ul./100 mg.

Effects of osmolality and oxygen availability on soluble cyclic AMP-dependent protein kinase activity of rat renal inner medulla.

“…As also shown in Table I, increases in cAMP and protein kinase activity ratios in response to alterations in the 02 content of the gas phase were clearly blunted as the osmolality of the incubation media was raised. At the higher media (19,31), that occur as a result of exposure of inner medulla to different osmolalities and 02 tensions do influence the precise quantitation of the comparisons of cAMP (Table II) (Table II) is consistent with previous findings (<15% change) using a combination of NADH+ oxidation and an 02 electrode to estimate 02 concentration (30). Thus, reduced 02 solubility did not account for the blunted cAMP and protein kinase responses to 02 over the range of 02 and media osmolality examined (Tables I, II).…”

“…Inner medullary 02 tension seldom exceeds 60 mm Hg (2,3) and osmolality in this region of the kidney is generally >500 mosM even during water diuresis (1,(19)(20)(21)31). The routine use of standard low osmolality buffers and high ambient 02 concentrations could artifactually increase basal kinase activity ratios and diminish the apparent sensitivity of this parameter to AVP stimulation in vitro.…”

Factors affecting the distribution of chloride ions in rat renal outer medulla.

“…Likewise there were no significant alterations in cell volume, calculated as described above (see also Law, 1975b). It was observed, however, that minor but consistent cellular swelling (approx.…”

“…The osmolality of this solution, and of all the modifications of it as described below, is 540 m-osmole/kg. H20, which is iso-osmolal with the tissue fluids of the outer medulla (Law, 1975b by Burg & Green (1973b). This complex will be referred to as EA-Cys.…”

Isovolumetric regulation of isolated S2 proximal tubules in anisotonic media.

“…Previous studies ofrenal volume regulation have used tissue slices, cell suspensions, isolated tubules, and single cells (1)(2)(3)(4)(5)(6)(7)(8)(22)(23)(24)(25)(26)(27)(28)(29)(30). In all of these studies the medium osmolality was changed suddenly, which is uncharacteristic of osmotic changes that might be encountered in pathophysiologic states in vivo.…”