P12 SOCII?TE BELGE DE PHYSIOLOGIE ET DE PHARMACOLOGJE

and a “K,” = 2.03 mM Glucose (i.e. the glucose concentration at which a half maxi- mal lactate production occurs).

The interpretation of these kinetic parameters is quite uncertain, partly because we don’t know the characteristics of the active and/or passive transports of glucose and lactate across the cell membranes, and partly because the conversion of glucose into lactate obviously varies with G. Indeed when G = 20, or even 5 mM, some of the glucose taken up will enter pathways that do not lead to lactate. By contrast, when G = 0.5 mM, a substantial amount of the lactate produced must arise from substrate(s) other than glucose. Amino acids, especially glutamine, are likely sources for this non-glycolytic lactate, as in some other cultured cells (ZIELKE et al., 1978). In this connection, it may be noted that our media contain glutamine (2.5 mM) and glutamate (about 1 mM).

Our value for U in the same range as those recently published by WHITE et al. (1983) for a variety of (non-endotheiial) cells, whereas our “K,” is about 4 times higher. The experimental procedures were, however, quite different, since these au- thors measured the initial rates of labelled D-Glucose uptake in cells that had been freshly suspended in a serum-free, simplified medium.

Acknowledgments. - We are indebted to Mrs. M. GILLET for her skillful technical assistance, and to the Fonds de la Recherche Scientifque Medicale for Grant 3.4555175.

References

BRACHET, E. A. (oo00) Arch. int. Physiol. Biochim. 90, P24-P25. BRUNK, C. E., JONES, K . C. & JAMES, T. W. (1979) Anal. Biochem. 92, 497-500. GRAHAM, D. & SMYDZUK, J . (1965) Anal. Biochem. 11, 246-255. LOWRY, 0. H. & PASSONNEAU, J . V. (1972) in A Flexible Method of Enzymatic Analysis, p. 195

WHITE, M. K . , BRAMWELL, M. E. & HARRIS, H. (1983) J . Cell. Sci. 62, 49-80. ZIELKE, H . R. , OWND, P. T., TILDON, J . T., SEVDALIAN, D. A . & CORNBLATH, D. (1978) J. Cell.

Academic Press, New York.

Physiol. 95, 41-48.

A. KAHN and E. BRACHET (Dkpartement de Pkdiatrie, et Laboratoire de Patho- physiologie, Universitk Libre de Bruxelles, B-1000 Bruxelles).

Hydrocortisone prevents the increases in permeability and PGE synthesis induced by endotoxin in the isolated rat mesentery.

We have shown earlier that endotoxin (ETX) increases the permeability coeffi- cient of albumin (PA), and the synthesis of prostaglandin E (PGE) in the rat me- sentery (BRACHET & KAHN, 1981). As these effects could be inhibited by indometha- cin, we had suggested that most, if not all, of the early actions of endotoxin in the mesentery could be ascribed to the local triggering of PGE synthesis. The present experiments were designed as a complement to those cited above. We investigated whether hydrocortisone (HC) might also block the rises in PA and PGE produc- tion, induced by ETX. Glucocorticoids eventually inhibit phospholipase A, (FLOWER, 1981), and block PG synthesis through other mechanisms than indomethacin.

To determine PA, a small sheet of mesentery is stretched over the window (dia- meter : l cm) that separates the two halves of a diffusion cell. Each compartment

Arc

hive

s of

Phy

siol

ogy

and

Bio

chem

istr

y D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y U

nive

rsity

of

Mel

bour

ne o

n 10

/27/

14Fo

r pe

rson

al u

se o

nly.

REUNION DE BRUSSEL, FEVRIER 1984 P13

thus defined contains 2 ml of Hank’s solution, with 1 mg/ml albumin. A tracer amount of [1*51] Albumin is then added to one chamber, and PA may be derived from the rate of equilibration of the tracer (KAHN & BRACHET, 1979).

The following types of incubation were defined : a 30-min preincubation without (Group I), or with (Group 11) HC, 20 pg/ml, followed by either ETX, 50 pg/ml (Sub- groups A), or no ETX (Subgroups B). In Group I1 C, hydrocortisone was added 1 min after ETX.

Results were (in cm/s x lo+) : 8.37 f 0.68 (IA), 5.98 f 0.51 (IB), 5.76 f 0.72 (IIA), 5.94 f 0.51 (IIB), and 8.37 f 0.68 (IIC). Each group comprised 20 to 24 mesenteries.

PGE synthesis was measured in sheets of mesentery having the same dimensions as those used to determine PA, preincubated 30-min HC, with 20 pg/ml (HC +), or without (HC-). ETX was then added to half the tubes in both groups (50 pg/ml). Incubations were stopped 10 min thereafter, and PGE were assaied as described el- sewhere (BRACHET & KAHN, 1981). PGE levels were (ng/mesentery) : 4.49 k 0.20 (HC-, ETX-), 8.69 f 0.27 (HC-, ETX + ), 4.04 f 0.27 (HC + , ETX-), and 4.29 f 0.23 (HC+ , ETX+). Each group represents 40 to 42 mesenteries.

The rises in PGE and PA, induced by ETX, were of the same magnitude as tho- se reported earlier (BRACHET & KAHN, 1981). The absolute levels are, however twice higher, this discrepancy may be ascribed to a change in our supply of anti-PGE se- rum (Miles- Yaeda instead of Calbiochem). These results point again to the impor- tance of PGE synthesis as an early event of ETX action in the mesentery.

If we consider the similarities shared by the mesentery and vascular endothelium, our results might suggest that glucocorticoids might be more effective as preventive, rather than curative agents in the treatment of septic shock, where increases in vas- cular permeability are likely to occur.

Acknowledgments. - We are indebted to Mrs. M. GILLET for her technical help. This work was sup- ported by Grant 3.4555/75 from the Fonds de la Recherche Scienlifque Medicate.

References

BRACHET, E. & KAHN, A. (1981) Biochim. Biophys. Acta 673, 495-503. FLOWER, R. (1981) Trends Pharmacol. Sci. 2, 186-189. KAHN, A. & BRACHET, E. (1979) Biochim. Biophys. Acta 588, 219-231.

W. ZEISKE (Institut fur Tierphysiologie und Angewandte Zoologie der Freien Universitat Berlin, Grunewaldstr. 34, D-1000-Berlin 41, F. R . G.) .

Irreversible block of Na’ transport in frog skin by T1’ ions.

Apical membrane K‘ channels in frog skin (Rana temporaria) are permeable for NH.,’, Rb+, and T1’ ions (ZEISKE & VAN DRIESSCHE, 1983). The ionic current through these channels is impaired after prolonged exposure to mucosal Tl’. In the skin of other frogs the outer membrane is permeable for Na’ ions only. Here, serosal appli- cation of millimolar concentrations of T1’ results in a slow but irreversible decrease in Na’ current (chloride-free solutions). After a sudden concentration jump with mu- cosal sodium, Na’,, transcellular sodium current, INa, rises alinost instantaneously to a peak from where it relaxes to a plateau value within seconds (“recline”

Arc

hive

s of

Phy

siol

ogy

and

Bio

chem

istr

y D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y U

nive

rsity

of

Mel

bour

ne o

n 10

/27/

14Fo

r pe

rson

al u

se o

nly.