Inhibition of choline acetyltransferase by excess cysteine

Distribution of choline acetyltransferase in cerebral and extracerebral cranial arteries of the cat. Its relationship to neurogenic atropine-sensitive dilation

Choline-acetyltransferase (ChAT) activity was surveyed in segments of cranial arteries--both cerebral and extracerebral--from the cat. High levels were found in pial arteries, both cerebral and cerebellar, and in the arteries to salivary glands, tongue, and nose. Intermediate levels were found in the external and internal maxillary arteries and many of their branches. Enzyme levels in the arteries supplying the head--common carotid, vertebral, and in several systemic arteries and veins and also the lingual vein--were probably not significant. Only those vessels that have higher ChAT contents show capacity for neurogenic vasodilation. The dilation of segments of a number of these arteries, the basilar, middle cerebral, lingual, and internal maxillary, is reduced significantly by atropine (5 X 10(-7) M). ChAT activity did not correlate with vessel norepinephrine content. The data may be interpreted as defining a functional vasodilator system to the head encompassing both cerebral and extracerebral arteries that depends in part on a functional cholinergic link involving a muscarinic receptor. It is separate from the adrenergic outflow. The tissues supplied by vasculature receiving this type of innervation are of ectodermal origin.

The 'compartmentation' of choline acetyltransferase within the synaptosome

1. Choline acetyltransferase may be isolated in either a bound or soluble form after hypo-osmotic treatment of a crude synaptosome fraction, depending on the conditions. 2. In the bound form, the enzyme appears to be associated with the larger membrane fragments rather than with synaptic vesicles. 3. The bound form is predominant at slightly acid pH values and low ionic strength, the soluble form under more physiological conditions of pH and ionic strength. 4. Sodium chloride, potassium chloride, magnesium chloride and calcium chloride at similar ionic strengths solubilize the enzyme. 5. Choline acetyltransferase was found to be soluble under these conditions after release from synaptosomes from rat and pigeon cerebra, guinea-pig cortex and rabbit cortex, caudate nuclei, diencephalon and midbrain. 6. Certain isoenzymes of lactate dehydrogenase behaved similarly.