Effects of phospholipase A2 on numbers of histamine H1 receptors in guinea pig lungs.
Effects of phospholipase A2 on numbers of histamine H1 receptors and muscarinic acetylcholine receptors were estimated in guinea pig lungs. Histamine H1 and muscarinic acetylcholine receptors in lung membranes were studied by the direct binding technique using 3H-pyrilamine and 3H-quinuclidinyl benzilate, respectively. The control group had two orders (high-affinity and low-affinity) of binding sites of histamine H1 receptors. Pretreatment of lung membranes with phospholipase A2 destroyed high-affinity binding sites, and these sites could not be detected after treatment. Low-affinity sites were not affected by the treatment. In contrast, the numbers of muscarinic acetylcholine receptors did not change significantly in spite of the addition of phospholipase A2. These results indicate that resistance of receptors against phospholipase A2 treatment varies among receptors and even between the binding sites in the same receptor. These variations might modulate pathological conditions associated with inflammation in which phospholipase is activated. Easy establishment of histamine tachyphylaxis might be explained by this mechanism.
Hayashi
K
K
Department of Internal Medicine, Faculty of Medicine, University of Nagoya, Japan.
Sugiyama
S
S
Takagi
K
K
Satake
T
T
Ozawa
T
T
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D006168:Guinea Pigs; D008168:Lung / Q000378:metabolism*; D008297:Male; D010740:Phospholipases / Q000494:pharmacology*; D010741:Phospholipases A / Q000494:pharmacology*; D054467:Phospholipases A2; D011738:Pyrilamine / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011969:Receptors, Histamine H1 / Q000187:drug effects / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism
D011969:Receptors, Histamine H1; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D011738:Pyrilamine