Showing papers by "Peter C. M. Molenaar published in 1982"

Neural and non-neural acetylcholine in the rat diaphragm.

Abstract: The compartmentation of acetylcholine (ACh) and of choline acetyltransferase in the rat diaphragm was analysed by measuring their contents in muscle segments containing endplates (e.p.) and endplate-free segments (non-e.p.) at different times following section of the phrenic nerve. In addition ACh release was determined before and after denervation. Freshly dissected hemidiaphragms contained about 125 pmol of ACh; more than 90% of this was localized in the e.p. portion. Between 10 and 18 h after denervation the ACh content of the e.p. portion decreased by 80% and its ACh concentration became approximately equal to that in the non-e.p. region, whose ACh content did not change. Spontaneous release of ACh was reduced by denervation and ACh release evoked by 50 mM KCl was practically abolished. Choline acetyltransferase activity in freshly dissected preparations was about 30 nmol of ACh per gram per hour, K$_{\text{m}}$ 0.5 mM. About 65% of the enzyme disappeared in the first 24 h and the remaining 35% between 24 and 50 h after denervation. A different enzyme capable of ACh synthesis was found in the muscle fibres; its activity did not decrease after denervation. It is concluded that about 70% of the ACh in the diaphragm is contained in the motor nerve terminals, about 10% in the intramuscular nerve fibres and the remainder in the muscle fibres, and that about 65% of choline acetyltransferase is in the motor terminals and 35% in the nerve fibres.

Free and bound acetylcholine in frog muscle.

Abstract: 1. Frog sartorius muscles were divided into end-plate containing (e.p.) and end-plate-free (non-e.p.) segments or homogenized in Ringer solution at 0 degrees C in the presence or absence of added acetylcholinesterase from electric eel. ACh was extracted from the tissue or from the homogenates and measured by mass fragmentography. 2. The concentration of ACh in non-e.p. segments was about six times lower than that in e.p. segments. 3. Homogenization of muscles in Ringer caused the hydrolysis of a small fraction ('free-1') of total ACh; addition of extra acetylcholinesterase caused hydrolysis of another, greater, fraction ('free-2' ACh). The esterase-resistant ('bound') ACh was stable at 0 degrees C up to 15 min of incubation. 4. Denervation for 15 days, which caused the disappearance of the nerve terminals, did not influence ACh in non-e.p. segments, but reduced total and bound ACh by about 75%, and free-2 ACh by 90%. 5. Treatment with La3+ ions, which caused the disappearance of synaptic vesicles, did not influence total ACh, but reduced bound ACh by 75%, whereas free-1 and free-2 ACh were increased. 6. Electrical stimulation of the nerve at 5 sec-1 or incubation with 50 mM-KCl did not affect ACh in the non-e.p. segments, but reduced by roughly 60% total, bound, and free ACh. 7. It is concluded that about 75% of bound ACh derives from synaptic vesicles, corresponding to 11,000 molecules per vesicle, and 25% from non-neural ACh; that free-1 and free-2 ACh derive mainly from the nerve terminal cytoplasm, although they may be contaminated by vesicular ACh.

Eaton-Lambert syndrome: acetylcholine and choline acetyltransferase in skeletal muscle.

Abstract: In biopsied intercostal muscle from six patients with Eaton-Lambert syndrome, we measured acetylcholine content and release and choline acetyltransferase. Both the spontaneous and the KCl-evoked release of acetylcholine were abnormally low. On the other hand, the acetylcholine content and the level of choline acetyltransferase activity were within the range of values earlier found in healthy human intercostal muscle. These results are consistent with the view that the defect in this syndrome lies not in the synthesis or storage of the transmitter but in the mechanism of release itself.