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Effects of polyamines on cyclic AMP‐mediated stimulation of amino acid transport in isolated rat hepatocytes
Author(s) -
Auberger Patrick,
Samson Michel,
Cam Ginette Le,
Cam Alphonse Le
Publication year - 1983
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041170211
Subject(s) - putrescine , spermine , spermidine , polyamine , stimulation , amino acid , cadaverine , biochemistry , leucine , chemistry , biology , enzyme , endocrinology
The effects of natural polyamines on cyclic AMP‐mediated stimulation of amino acid transport in isolated rat hepatocytes were analyzed. Despite the fact that polyamines could directly compete with α‐aminoisobutyric acid (AIB) for uptake, preincubation of hepatocytes with polyamines did not significantly alter basal AIB transport. The stimulatory effect of glucagon or cyclic AMP analogs was differently affected by polyamines, since it was reduced in the presence of spermine and, inversely, potentiated by spermidine, putrescine, and cadaverine. Dose‐dependence analysis showed that half maximal and maximal effects occurred with 2–3 and 6–10 mM external concentrations, respectively. None of the polyamine effects could be ascribed to transstimulation or transinhibition of amino acid uptake. The inhibitory effect exerted by spermine correlated its capacity to inhibit [ 3 H]‐leucine incorporation into proteins partially. The potentiating effect of the other polyamines did not result from stabilization of newly synthesized carrier proteins. Instead, the increase in V max of the high affinity transport component suggested that more carriers became available, presumably because polyamines facilitated their synthesis by interacting directly with one or several steps controlled by cyclic AMP. Polyamines appear to represent a new class of factors capable of modulating the cyclic AMP‐mediated stimulation of amino acid transport, in hepatocytes.