The inulin space, solute concentrations, and weight changes in rat renal medullary slices incubated in iso‐osmolal media, and their modification during anoxia and hypothermia.

Abstract

1. The volume of distribution of [14‐C]carboxyl inulin has been studied in slices of outer and inner medulla from rat kidney incubated in Krebs phosphate‐bicarbonate Ringer, modified to render it iso‐osmolal with the tissue fluids in these zones, under three conditions, (a) aerobically at 37 degrees C (control), (b) anoxically at 37 degrees C, and (c) aerobically at 0 degrees C. 2. Under control conditions near steady‐state volumes of approximately 24 and 42 mul./100 mg wet weight slice were obtained for outer and inner medulla respectively during the period 10–30 min from the start of incubation. In the outer medulla the volumes of distribution in anoxic and hypothermic slices exceeded that in control slices during this time, but control values increased from 30 to 100 min so that after 100 min the distribution volumes were approximately 30 mul./100 mg under each set of conditions. 3. In the inner medulla control and anoxic slices had inulin distribution volumes of approximately 42 mul./100 mg during 10–30 min, rising to over 50 mul./u99 mg by 100 min. Slices incubated hypothermically reached a steady‐state value of approximately 40 mul./100 mg by 30 min, which did not increase further for up to 100 min. 4. All slices lost about 10% of their initial weight during the first 3 min of incubation. Thereafter control slices maintained weight constancy for at least 30 min (outer medulla) or 100 min (inner medulla); slices incubated anoxically or hypothermically gained weight, the gains being greatest in anoxic outer and hypothermic inner medulla. 5. The K concentration within control slices (both zones), hypothermic outer and anoxic inner medulla attained equilibrium when slice [K] was approximately 8 times medium [K] (5–9 mM). In anoxic outer and hypothermic inner medullary slices [K] fell to a significantly greater extent, but interpretation of these findings in terms of slice K loss is subject to modification in respect of the increases in slice weight (water content) accompanying the [K] decreases. 6. There was a transient (1–3 min) rise in [Na] in all slices. This was followed by a [Na] decrease, which was most apparent in control slices, and finally a gradual increase towards medium [Na] (141 and 180 mM for outer and inner medulla respectively).

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.…”

“…Buffer with a total osmolality of 1,650 mosM contained 365 mM Na+ (340 mM NaCl) and 900 mM urea, whereas that with a total osmolality of 2,000 mosM contained 425 mM Na+ (400 mM NaCl) and 1,130 mM urea. The latter two buffers were studied because the total osmolalities, sodium, and urea contents resembled those reported in rat inner medulla during water deprivation (1,(19)(20)(21). In some experiments, buffers were prepared to assess effects of urea and NaCl separately (see Results).…”

Calcium-dependent action of osmolality on adenosine 3',5'-monophosphate accumulation in rat renal inner medulla: evidence for a relationship to calcium-responsive arachidonate release and prostaglandin synthesis.

“…In the present study, we examined the possibility that the effects of osmolality on rat inner medullary cAMP metabolism might be related to changes in prostaglandin synthesis. Consistent with the solute content of inner medulla (10,11), urea was employed as a major component of the high osmolality media.…”

pH and temperature dependence of glutamine uptake, carbon dioxide and ammonia production in kidney slices from acidotic rats.

“…A small portion of each slice was removed, weighed and dried overnight at 100°( ' to determine the total water content of slices. Law (1975 Lemieux & Gougoux, 1979). It was not the concern of this study to determine what the end products were, but rather to attempt to evaluate the effects of medium pH, temperature and acidosis on influx of glutamine into the tissue.…”