Characteristics of L-carnitine transport by lactating rat mammary tissue

• Published in: Biochimica et biophysica acta Vol. 1393; no. 1; pp. 49 - 56
• Main Authors: Shennan, D.B., Grant, A., Ramsay, R.R., Burns, C., Zammit, V.A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 31-07-1998
• Subjects: Animals; Biological Transport; Carnitine - metabolism; Culture Techniques; Female; Kinetics; l-Carnitine; Lactation; Mammary gland; Mammary Glands, Animal - metabolism; Mammary Glands, Animal - pathology; Rats; Rats, Wistar; Sodium - metabolism; Sodium dependence; Substrate Specificity; l-Carnitine; Sodium dependence; Mammary gland
• ISSN: 0005-2760; 0006-3002; 1879-145X
• DOI: 10.1016/S0005-2760(98)00056-3

The transport of
l-carnitine by lactating rat mammary tissue has been examined.
l-Carnitine uptake by rat mammary tissue explants isolated from lactating rats, 3–4 days post partum, was via both Na
+-dependent and Na
+-independent pathways. The Na
+-dependent pathway, the predominant route for
l-carnitine uptake, was a saturable process: the
K
m and
V
max were, respectively, 132 μM and 201 pmol/2 h/mg of intracellular water. The Na
+-independent pathway, which was non-saturable, had a coefficient of 0.26 μl/mg of intracellular water/2 h. The Na
+-dependent component of
l-carnitine uptake by mammary tissue explants was
cis-inhibited by
d-carnitine and acetyl-
l-carnitine, but not by choline or taurine. In contrast, the Na
+-independent component of
l-carnitine uptake was not affected by any of these compounds. The uptake of
l-carnitine by mammary tissue isolated from lactating rats, 10–12 days post partum, was qualitatively similar to that by mammary tissue taken from rats during the early stage of lactation. However,
l-carnitine uptake was quantitatively lower: this was attributable to a reduction in the Na
+-dependent component of
l-carnitine uptake.
l-Carnitine efflux from rat mammary tissue taken from animals 3–4 days post partum, consisted of at least two components; a fast extracellular component and a slow membrane-limited component. Reversing the
trans-membrane Na
+-gradient did not stimulate
l-carnitine efflux suggesting that the Na
+-dependent
l-carnitine carrier operates with asymmetrical kinetics. A hyposmotic shock, hence cell-swelling, increased
l-carnitine efflux from mammary tissue explants.