Abstract

Norepinephrine (8 mM) produced a rapid and readily reversible rounding and vacuolation in mouse peritoneal macrophages. The rapid onset and offset of these changes suggested something other than classical pinocytosis as a mechanism. The morphological changes were inhibited by cytochalasin B but not by propranolol. Norepinephrine lowered the contact angle between a macrophage monolayer and a sessile drop of saline. This indication of increased membrane hydrophilicity is consistent with an increase in membrane surface pressure. Norepinephrine had no effect on neutral phospholipid (phosphatidylcholine) monolayers but expanded acidic phospholipid (phosphatidylserine) monolayers over a wide range of surface pressures (15-40 dynes/cm). Based on these observations, it is suggested that norepinephrine may produce the morphological changes by expanding the macrophage membrane to the point of membrane buckling and/or by a viscotropic stimulation of membrane enzymes which, in turn, activate microfilaments.