EFFECT OF PLATELET-ACTIVATING-FACTOR ON BASAL AND INSULIN-MEDIATED SYSTEM-A AMINO-ACID-TRANSPORT IN RAT SOLEUS MUSCLE

We investigated the effect of platelet-activating factor (PAF) on basa l and insulin-stimulated sodium-dependent neutral amino acid transport by system A in rat soleus muscle. Fasted male Sprague-Dawley rats (75 -100 g) were given an intravenous injection of saline or PAF (4 mug/kg ) and killed 1 hr later. Isolated soleus muscles were incubated in med ia containing 1-C-14-alpha-aminoisobutyric acid (AIB; system A amino a cid analog), H-3-inulin, and 0 (basal) or 100 mU/ml insulin. Na+-free media were assessed by Na+-independent AIB uptake. The rate of AIB upt ake by muscle was corrected for uptake into extracellular (inulin) spa ce. Basal cellular AIB uptake by soleus muscles from PAF-treated rats was 30.2% lower than in controls. Insulin increased the absolute rate of cellular AIB uptake above basal levels to the same extent in muscle s of control and PAF-treated rats, although the rate of maximal insuli n-stimulated AIB uptake was 20% lower in muscles of PAF-treated rats. Na+-independent AIB uptake (measured in Na+-free media) was the same i n muscles of control and PAF-treated rats. The fact that AIB uptake in Na+-free media was the same in muscles of control and PAF-treated rat s indicates that the reduction in basal and insulin-stimulated AIB upt ake in muscles of PAF-treated rats was due to an alteration of system A Na+-dependent amino acid transport.