Epithelial brush-border membrane vesicles (BBMVs) from the hepatopancreas of the lobster Homarus americanus were prepared using a magnesium precipitation technique and employed in transport experiments designed to demonstrate the effects of external and internal divalent cationic heavy metals on the uptake of l-[(3)H]proline. When BBMVs were exposed to a high external concentration (2.5 mmol l(−)(1)) of Cd(2+), Cu(2+), Fe(2+), Mn(2+) or Zn(2+), l-[(3)H]proline (0.5 mmol l(−)(1)) uptake was significantly (P<0.05) decreased by each metal. However, if a 30 min pre-incubation period with each metal was used before incubation of the vesicles with amino acid and metal, a significant (P<0.05) enhancement of l-[(3)H]proline transport occurred. Zinc was the most stimulatory metal of those tested. Proline influxes (1.0 and 2.5 mmol l(−)(1)) were hyperbolic functions of bilateral [Zn(2+)], with a lower apparent zinc half-saturation constant (K(m)) at the higher amino acid concentration. l-[(3)H]proline influx was a hyperbolic function of external [l-proline] (K(m)=2.10+/−0.26 mmol l(−)(1); J(max)=2290+/−600 pmol mg(−)(1)protein 10 s(−)(1)) (means +/− s.e.m., N=3), and bilateral exposure to zinc significantly (P<0.05) increased the maximal rate of influx, J(max), of proline (J(max)=4890+/−250 pmol mg(−)(1)protein 10 s(−)(1)), but had no effect (P>0.05) on apparent l-[(3)H]proline binding to the membranes (K(m)=1.66+/−0.23 mmol l(−)(1)) (means +/− s.e.m., N=3). In the presence of 0.5 mmol l(−)(1)l-pipecolate, bilateral zinc-stimulated, carrier-mediated, l-[(3)H]proline influx was abolished. At low external concentrations of zinc alone (e.g. below 1.0 mmol l(−)(1)), l-[(3)H]proline influx was enhanced by the metal. Enhanced amino acid uptake in the presence of external zinc alone was abolished by l-pipecolate. A model accounting for external and internal zinc enhancements of l-[(3)H]proline influx by the Na(+)-dependent l-pipecolate-sensitive IMINO transport system in these membranes is proposed.

REFERENCES

Ahearn
G. A.
,
Behnke
R. D.
(
1991
).
L-Proline transport systems of starfish pyloric caeca
.
J. Exp. Biol
158
,
477
–.
Ahearn
G. A.
,
Gerencser
G. A.
,
Thamotharan
M.
,
Behnke
R. D.
,
Lemme
T. H.
(
1992
).
Invertebrate gut diverticula are nutrient absorptive organs
.
Am. J. Physiol
263
,
472
–.
Ahearn
G. A.
,
Grover
M. L.
,
Dunn
R. E.
(
1985
).
Glucose transport by lobster hepatopancreatic brush border membrane vesicles
.
Am. J. Physiol
248
,
133
–.
Ahearn
G. A.
,
Monckton
E. A.
,
Henry
A. E.
,
Botfield
M. C.
(
1983
).
Alanine transport by lobster hepatopancreatic cell suspensions
.
Am. J. Physiol
244
,
150
–.
Ahearn
G. A.
,
Zhuang
Z.
,
Duerr
J.
,
Pennington
V.
(
1994
).
Role of the invertebrate electrogenic 2Na+/1H+antiporter in monovalent and divalent cation transport
.
J. Exp. Biol
196
,
319
–.
Behnke
R. D.
,
Wong
R. K.
,
Huse
S. M.
,
Reshkin
S. J.
,
Ahearn
G. A.
(
1990
).
Proline transport by brush border membrane vesicles of lobster antennal glands
.
Am. J. Physiol
258
,
311
–.
Bettger
W. J.
,
O'Dell
B. L.
(
1981
).
A critical physiological role of zinc in the structure and function of biomembranes
.
Life Sci
28
,
1425
–.
Daniel
H.
,
Adibi
S. A.
(
1995
).
Selective effect of zinc on uphill transport of oligopeptides into kidney brush border membrane vesicles
.
FASEB J
9
,
1112
–.
Giroux
E. L.
,
Henkin
R. I.
(
1972
).
Competition for zinc among3010serum albumin and amino acids
.
Biochim. Biophys. Acta
373
,
64
–.
Hopfer
U.
,
Nelson
K.
,
Perrotto
J.
,
Isselbacher
K. J.
(
1973
).
Glucose transport in isolated brush border membrane from rat small intestine
.
J. Biol. Chem
248
,
25
–.
Kessler
M.
,
Acuto
O.
,
Storelli
C.
,
Murer
H.
,
Muller
M.
,
Semenza
G.
(
1978
).
A modified procedure for the rapid preparation of efficiently transporting vesicles from small intestinal brush border membranes. Their use in investigating some properties of D-glucose and choline transport systems
.
Biochim. Biophys. Acta
506
,
136
–.
Prasad
A. S.
(
1979
).
Clinical, biochemical and pharmacological role of zinc
.
Annu. Rev. Pharmac. Toxicol
20
,
393
–.
Stevens
B. R.
,
Wright
E. M.
(
1985
).
Substrate specificity of theintestinal brush border proline/sodium (IMINO) transporters
.
J. Membr. Biol
87
,
27
–.
Vallee
B. L.
,
Falchuck
K. H.
(
1993
).
The biochemical basis of zinc physiology
.
Physiol. Rev
73
,
79
–.
Vilella
S.
,
Cassano
G.
,
Storelli
C.
(
1989
).
How many Na+-dependent carriers for L-alanine and L-proline in the eel intestine? Studies with brush border membrane vesicles
.
Biochim. Biophys. Acta
984
,
188
–.
Wapnir
R. A.
,
Khani
D. E.
,
Bayne
M. A.
,
Lifshitz
F.
(
1983
).
Absorption of zinc by the rat ileum: effects of histidine and other low molecular weight ligands
.
J. Nutrit
113
,
1346
–.
Wapnir
R. A.
,
Stiel
L.
(
1986
).
Zinc intestinal absorption in rats: specificity of amino acids as ligands
.
J. Nutrit
116
,
2171
–.
This content is only available via PDF.