Neural regulation of cholinesterase in newt skeletal muscle. II. The effects of denervation and of culture in vitro

Abstract The effect of denervation in vivo on the acetylcholinesterase (AChE) of newt ( Notophthalrnw uiridescens ) triceps muscle was compared with the effect of culturing explanted muscles in organ culture. Two weeks after denervation, the AChE activity of triceps muscles falls to approximately 60% of that in innervated muscles. The initial rate of loss of AChE is more rapid during summer than during winter, but no seasonal differences were observed in the specific activity of AChE in innervated muscles or in muscles two weeks after denervation. Changes in AChE activity when the triceps muscles were maintained in organ culture were similar in rate and in extent to those that occurred after denervation in vivo. The effect of denervation in vivo and culturing upon the individual AChE species separated by velocity sedimentation was also determined. Denervation and organ culture both resulted in a marked and rapid loss of two forms of AChE with sedimentation coefficients of 16.5S and 12.8S on sucrose density gradients. The former is associated with the motor endplates and the latter with the musculotendinous junctions. The activity of another form of AChE, with a sedimentation coefficient of 9.8S, transiently increased after denervation, but after one week returned to the initial level. The activity of a major form of AChE, with a sedimentation coefficient of 5,5S, remained constant after denervation, but that of the slowest sedimenting form (3.7S) declined slightly after one week. Similar alterations in the activities of these forms were observed in cultured muscles. Co‐culture of the muscles with dorsal root (sensory) ganglia from newts prevented both the loss of total AChE activity and the alterations in molecular forms of AChE in the muscles. This innervation‐like effect of the ganglia is apparently mediated by a diffusible factor(s) since ganglia separated from the muscles by a Millipore filter (0.22 μm pore size) also prevented alterations in AChE activity and molecular forms in the cultured muscles. These results demonstrate that the response of AChE to the absence or presence of nervous tissue, apparently mediated by a neurotrophic factor, is identical to that observed in vivo, at least in the case of the characteristics examined.