Abstract
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 ( K m = 112.5 ± 19.7 μM; V max = 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 ( K m = 18.1 ± 4.9 μM; V max = 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.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Biomembranes
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