1. The mean channel open time (tau) of ACh receptors in adult developing rat skeletal muscle was estimated by analysis of ACh current fluctuations. 2. At adult end-plates, tau was 1.4 msec at 21 degrees C. Time constants of miniature end-plate current decays (taus) were equally brief. 3. On the other hand, tau and taus were long (4.5 msec, 21 degrees C) at neonatal rat end-plates. These estimates are comparable to values obtained at extrajunctional sites on embryonic rat myotubes grown in culture and on adult denervated muscle fibres. 4. Both tau and taus decreased to values characteristic of adult end-plates during the first 2 weeks after birth. 5. Complex ACh power spectra were obtained at most end-plates during the transition period and at some, miniature synaptic current decays were doubly exponential. End-plates in transition might contain a mixture of slow, neonatal channels and fast, adult channels.

A post-natal decrease in acetylcholine channel open time at rat end-plates.

The aims of the studies reported here were to determine the extent to which the specializations induced by agrin on cultured chick myotubes resemble the postsynaptic apparatus and examine how these specializations form. We found that agrin induces the formation of specializations at which at least 6 components of the postsynaptic apparatus are concentrated: one cytoplasmic component [a 43 kDa acetylcholine receptor (AChR)-associated protein], 3 membrane components [AChRs and globular forms of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)], and 2 extracellular matrix-associated proteins (A12 asymmetric AChE and a heparan sulfate proteoglycan). The accumulation of AChE and BuChE into agrin-induced aggregates occurred in the absence of any change in the amount, rate of synthesis, accumulation, and release, or molecular forms of either enzyme. Thus, agrin affects primarily the distribution of these components of the postsynaptic apparatus and not their metabolism. Agrin-induced formation of AChR aggregates was not prevented by inhibition of protein synthesis, consistent with our previous results that agrin-induced accumulation of AChRs occurs by lateral migration. The accumulation of components of the extracellular matrix would seem less likely to occur by lateral migration and so might require release of newly synthesized proteins; indeed, formation of aggregates of heparan sulfate proteoglycan was prevented by inhibitors of protein synthesis. Thus, different components of the postsynaptic apparatus accumulate in agrin- induced specializations by different mechanisms.

Agrin-induced specializations contain cytoplasmic, membrane, and extracellular matrix-associated components of the postsynaptic apparatus.

Specificity and plasticity of neuromuscular connections: Long-term regulation of motoneuron function

Be my guest: two acyclic cucurbit[n]uril-type receptors that carry SO(3) (-) -groups bind tightly to several commonly used neuromuscular blocking agents, such as rocuronium, in aqueous solution as revealed by direct and competitive UV/Vis binding assays. One of these containers functions as a potent reversal agent for rocuronium-induced neuromuscular block in rats.

Živa Majcen

Papers

A comparison of the effect of cholinesterase inhibitors on end-plate current and on cholinesterase activity in frog muscle.

The inhibition of frog tissue cholinesterases and the influence of eserine and prostigmine on the action of acetylcholine on the frog heart.

Kinetics of muscarinic cholinoreceptors and of acetylcholinesterase of frog heart ventricle under the influence of atropine.