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Induction of membrane alterations by norepinephrine: studies with macrophages and phospholipids monolayers
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.
Insights
Norepinephrine causes rapid, reversible changes in mouse macrophages, suggesting a novel mechanism beyond pinocytosis. These effects are linked to membrane expansion and microfilament activation.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Norepinephrine is a key neurotransmitter and hormone.
- Macrophage morphology is dynamic and responsive to external stimuli.
- Understanding cellular responses to norepinephrine is crucial in immunology.
Purpose of the Study:
- To investigate the rapid morphological changes induced by norepinephrine in mouse peritoneal macrophages.
- To elucidate the underlying cellular mechanisms responsible for these norepinephrine-induced alterations.
Main Methods:
- Treatment of mouse peritoneal macrophages with norepinephrine (8 mM).
- Assessment of morphological changes (rounding, vacuolation) and their reversibility.
- Inhibition studies using cytochalasin B and propranolol.
- Contact angle measurements to assess membrane hydrophilicity.
- Expansion of phospholipid monolayers (neutral and acidic) by norepinephrine.
Main Results:
- Norepinephrine induced rapid and reversible rounding and vacuolation in macrophages.
- These morphological changes were inhibited by cytochalasin B but not propranolol.
- Norepinephrine decreased the contact angle, indicating increased membrane hydrophilicity.
- Norepinephrine expanded acidic phospholipid monolayers but not neutral ones.
Conclusions:
- The observed macrophage changes suggest a mechanism distinct from classical pinocytosis.
- Norepinephrine's effects may involve membrane expansion leading to buckling or viscotropic stimulation of enzymes activating microfilaments.