[3H]Methotrexate as a ligand for the folate receptor of Dictyostelium discoideum.

Studies of the folate chemotactic receptor of vegetative Dictyostelium discoideum cells have been hampered by the presence of the degradative enzyme folate deaminase. The diaminopterin compounds aminopterin and methotrexate (MTX) are chemoattractants but are not attacked by the deaminase. [3',5',7,9-3H]methotrexate ([3H]MTX) is a nondegraded radioligand for the folate receptor.

Evidence for a pronounced secretion of cyclic AMP by Tetrahymena.

The unicellular eukaryote Tetrahymena pyriformis secretes significant amounts of cyclic AMP into its external medium. Cells transferred from growth medium into any of the following three different non-nutrient media: (a) 5 mM phosphate buffer containing 47 mM NaCl and 1 mM MgSO4, (b) 10 mM Tris, or (c) 1.3 mM Tris containing 1 mM citrate and 1 mM Ca(OH)2, released to the outside almost 60--80% of the total cyclic AMP produced during 2--5 h of incubation.

Increased levels of adenosine 3',5'-cyclic monophosphate in Tetrahymena stimulated by glucose and mediated by Ca2+ and epinephrine.

Stationary phase Tetrahymena cells exposed to 0.5-1% glucose experience an 8-fold increase in intracellular cyclic AMP within 1 hr. The increase follows an enhanced uptake of Ca2+ triggered by the glucose addition.

Membrane changes during growth of Tetrahymena in the presence of ethanol.

After a brief lag period for acclimation, Tetrahymena pyriformis, strain NT-1, is capable of growing in culture medium containing high levels of ethanol. When grown in a medium having 1.6% ethanol, the membrane phospholipid composition was significantly different from that of control cells.