The collagen-tailed or asymmetric forms (A) represent a major component of acetylcholinesterase (AChE) in the neuromuscular junction of higher vertebrates. They are hetero-oligomeric molecules, in which tetramers of catalytic subunits of type T (AChE T ) are attached to the subunits of a triple-stranded collagen "tail." We report the cloning of a rat AChE-associated collagen subunit, Q. We show that collagen tails are encoded by a single gene, COLQ. The ColQ subunits form homotrimers and readily form collagen-tailed AChE, when coexpressed with rat AChE T . We found that the same ColQ subunits are incorporated, in vivo, in asymmetric forms of both AChE and butyrylcholinesterase. A splice variant from the COLQ gene encodes a proline-rich AChE attachment domain without the collagen domain but does not represent the membrane anchor of the brain tetramer. The COLQ gene is expressed in cholinergic tissues, brain, muscle, and heart, and also in noncholinergic tissues such as lung and testis.Acetylcholinesterase (AChE, EC 3.1.1.7)1 is highly concentrated at vertebrate neuromuscular junctions. This enzyme is encoded by a single gene, and adult mammalian muscles express a single splice variant, corresponding to the catalytic subunit of type T (AChE T ) (1, 2). At the post-translational level, however, quaternary interactions introduce a considerable diversity of molecular forms that are characterized by distinct localizations in cellular structures. These molecules include amphiphilic monomers (G 1 a ) and dimers (G 2 a ), nonamphiphilic tetramers (G 4 na ), as well as hetero-oligomeric structures in which tetramers of catalytic subunits are disulfide-linked with a hydrophobic "tail" (20 kDa) in the membrane-bound G 4 a forms (3, 4) or with a collagenous "tail" in the collagen-tailed or asymmetric (A) forms. The latter molecules consist of one, two, or three tetramers (A 4 , A 8 , A 12 ), which are disulfide-linked to the strands of the triple helical collagen tail (see Fig. 1A). G 1 a and G 2 a forms appear to remain mostly intracellular and represent precursors of more complex molecules. The G 4 na form is secreted and hydrophobic-tailed tetramers (G 4 a ) are attached to the plasma membrane. The collagen-tailed molecules are tethered in the basal lamina, and are largely responsible for the high concentration of AChE at the neuromuscular junction.To understand the biosynthesis of the various AChE forms and its regulation, it is necessary to analyze the association of AChE T catalytic subunits with anchoring subunits, particularly the collagen subunits, which have been named Q, according to the nomenclature of AChE-associated proteins (5). Cloning and expression of the collagen tail subunit of the asymmetric AChE forms from Torpedo electric organ (tQ 1 ) allowed us to show that the structural and catalytic subunits assemble into collagen-tailed molecules when coexpressed in COS cells (6). The primary sequence of the Q subunit comprises an N-terminal region, Q N , a collagen domain, and a C-terminal domain, Q C . We showe...

The collagen-tailed forms of acetylcholinesterase (AChE) are accumulated at mammalian neuromuscular junctions. The A 4 , A 8 , and A 12 forms are expressed differently in the rat fast and slow muscles; the sternomastoid muscle contains essentially the A 12 form at end plates, whereas the soleus muscle also contains extrajunctional A 4 and A 8 forms. We show that collagen Q (ColQ) transcripts become exclusively junctional in the adult sternomastoid but remain uniformly expressed in the soleus. By coinjecting Xenopus oocytes with AChE T and ColQ mRNAs, we reproduced the muscle patterns of collagen-tailed forms. The soleus contains transcripts ColQ1 and ColQ1a, whereas the sternomastoid only contains ColQ1a. Collagentailed AChE represents the first evidence that synaptic components involved in cholinergic transmission may be differently regulated in fast and slow muscles.

Acetylcholinesterase (AChE) mRNA levels are severalfold higher in fast rat muscles compared with slow. We hypothesized that AChE mRNA levels and AChE activity in the neuromuscular junction depend on a specific nerve-induced pattern of motor unit activation. Chronic low-frequency stimulation, mimicking the activation pattern in slow muscles, was applied to fast muscles in rats. Molecular forms of AChE were analyzed by velocity sedimentation, and AChE mRNA levels were analyzed by Northern blots. AChE mRNA levels in stimulated fast muscles dropped to 10-20% of control after 1 week and became comparable to those in slow soleus muscles. The activity of the junctional A12 AChE form in 35 d stimulated fast muscles decreased to 56% of control value, reaching that in the soleus muscle. Therefore, synaptic AChE itself depends on the muscle activation pattern. Complete inactivity after denervation also decreased the AChE mRNA level in fast muscles to <10% in 48 hr. In contrast, profuse fibrillations observed in noninnervated immature regenerating muscles maintain AChE mRNA levels at 80% of that in the innervated fast muscles. If protein synthesis was inhibited by cycloheximide, AChE mRNA levels in 3-d-old regenerating muscle, still containing myoblasts, increased approximately twofold. No significant increase after cycloheximide application was observed either in denervated mature fast muscles or in normal slow muscles. Low AChE mRNA levels observed in those muscles are probably not caused by decreased stability of AChE mRNA as demonstrated in myoblasts.

The reasons for the relatively high failure rate after inferior alveolar nerve block in dentistry are not fully understood. Therefore, the effectiveness of different anesthetic solutions (2% and 4% lidocaine, 3% mepivacine, 2% and 4% articaine) in depressing the compound action potential amplitude of the sensory fibers in the rat sural nerve was examined under strictly controlled conditions in vitro. After application of an anesthetic solution and stimulation of the nerve with a supramaximal electrical stimulus, a complete disappearance of the compound action potential of the C fibers, but not of the A fibers, was observed in all the experimental groups. Both 2% and 4% articaine more effectively depressed the compound action potential of the A fibers than did other anesthetic solutions. These results are discussed in the light of recent clinical reports finding no differences in the effectiveness between 4% articaine and 2% lidocaine regarding the inferior alveolar nerve block.

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The characteristic response of Schwann cells (SC) accompanies peripheral nerve injury and regeneration. To elucidate their role, the question of whether or not regenerating axons can elongate across the segments of a peripheral nerve devoid of SC was investigated. Rat sciatic nerve was crushed so that the continuity of SC basal laminae was not interrupted. A segment about 15 mm long distal to the crush was either repeatedly frozen/thawed to eliminate SC or scalded by moist heat which, in addition, denatured the proteins in the SC basal laminae, too. Both sensory and motor axons grew rapidly across the frozen/thawed segment of the nerve. Their rate of elongation was reduced by only 30% in comparison to control crushed nerves. SC were not present along the path of growing axons adhering tightly to the bare SC basal laminae. The rate of elongation of regenerating sensory and motor axons in scalded nerve segments was eight times lower than in control crushed nerves. SC were present in that part of the scalded region that had been invaded by the regenerating axons but no further distally. These results suggest that acellular basal laminae of SC provide very good, although not optimal, conditions for elongation of regenerating sensory and motor axons. If biochemical integrity of the basal lamina is destroyed, the regenerating axons must be accompanied or preceded by viable SC. and axon elongation rate is significantly reduced.