ISSN:
1432-1912
Keywords:
Depolarization
;
Ion channels
;
Phosphatidylinositol
;
Inositol phosphates
;
Voltage-dependence
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary We have studied the accumulation of inositol phosphates (InsP) due to depolarization. A particulate preparation of rat brain was introduced to rule out transmitter activated mechanisms and to allow free access for drugs of high molecular weights. Potassium depolarization doubled InsP within a few minutes. InsP accumulation depended on time and K+ concentration, and was affected neither by tetrodotoxin nor by atropine. Radioactive metabolites co-eluted with inositol mono-phosphate and inositol bis-phosphate, whereas only minor amounts appeared with inositol tris-phosphate. The content in phosphatidylinositols was decreased. No evidence was found for the involvement of a neurotransmitter. Sea anemone toxin II (around 1 μmol/l), which keeps the Na+-channels open, promoted the InsP accumulation in an atropine-resistant manner. Tetrodotoxin prevented it when given before, and inhibited it when given after initiation by sea anemone toxin II. Moreover the K+ channel blockers 4-aminopyridine, dendrotoxin and tetraethylammonium all caused InsP accumulation. Palytoxin was by far the most potent promoter of InsP accumulation with a detection limit below 10 pmol/l, and displayed a unique bell-shaped concentration-effect correlation. Ouabain (3 μmol/l) and above) also elicited the InsP accumulation. The response to carbachol was not only inhibited completely by atropine, but also partially (more than 50%) by tetrodotoxin, which indicates the involvement of voltage-dependent sodium channels in the receptor-triggered InsP accumulation. Thus independent of the causative agent, depolarization promotes an InsP accumulation. We conclude that degradation of phosphatidylinositols is mediated not only by receptor occupation but also by a positive shift in membrane voltage.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00498733
