The mechanism of L-glutamate transport by lactating rat mammary tissue.
The transport of L-glutamate by lactating rat mammary gland has been examined using both tissue explants and a perfused mammary preparation. L-Glutamate uptake by mammary tissue explants was predominantly via a Na(+)-dependent pathway: Li+, choline+ and NMDG+ could not substitute for Na+. L-Glutamate efflux from preloaded explants was also influenced by the transmembrane Na(+)-gradient. These results are consistent with (Na(+)-glutamate) cotransport. The Na(+)-dependent system for L-glutamate transport in tissue explants was saturable (Km = 112.5 +/- 19.7 microM; Vmax = 71.3 +/- 10.4 nmol/min per g cells) and selective for anionic amino acids. Thus, D- and L-aspartate were high affinity inhibitors of L-glutamate uptake whereas neutral amino acids were relatively ineffective. D-Aspartate inhibited L-glutamate uptake in a competitive fashion. L-Glutamate uptake by the perfused mammary gland was (a) Na(+)-dependent (b) saturable (Km = 18.1 +/- 4.9 microM; Vmax = 40.3 +/- 3.7 nmol/min per g tissue) and (c) selective for anionic amino acids. The results suggest that the (Na(+)-glutamate) cotransporter is situated in the blood-facing aspect of the mammary epithelium.
Millar
I D
ID
Hannah Research Institute, Ayr, UK.
Calvert
D T
DT
Lomax
M A
MA
Shennan
D B
DB
D027322:Amino Acid Transport System X-AG; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002412:Cations; D005260:Female; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism*; D007700:Kinetics; D007774:Lactation; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism*; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000494:pharmacology; D027981:Symporters
D027322:Amino Acid Transport System X-AG; D002352:Carrier Proteins; D002412:Cations; D050491:Glutamate Plasma Membrane Transport Proteins; D027981:Symporters; D018698:Glutamic Acid; D012964:Sodium