Tilman Voigt

The T-tubular network and its triads in the sole plate sarcoplasm of the motor end-plate of mammals.

The transition between the subsynaptic folds and the T-tubules demonstrated in a former paper was further investigated in the sole plate area by using the extracellular marker Lanthanum. A tubular network of the T-system of the sole plate area which is connected to the subsynaptic folds and to the t-tubular elements between the myofibrils is described for the first time. T-tubules of this network criss-cross through the sarcoplasm of the sole plate and lie in close proximity to sole plate nuclei and mitochondria. Cisterns of sarcoplasmic reticulum of the sole plate area make contact with these t-tubules forming triads. The possible physiological role of this sole plate network and its triads will be discussed with regard to a transport of substances in tubules with the dimension of nanotubes and Ca2+ activated processes in the sole plate area.

Junctions between subsynaptic folds and rough sarcoplasmic reticulum of muscle fibres

Serial sections through motor end plate regions of mouse muscle fibres demonstrated junctions between the subsynaptic folds and the rough sarcoplasmic reticulum of the sole plate nuclei. The shape of these structures resembles that of the well-known peripheral couplings, diads and triads of muscle fibres. However, the location of the new junctions between the surface membrane and the sole plate nuclei at a large distance from myofibrils, indicates a different function. The connection with the rough sarcoplasmic reticulum possibly influence the regulation of fibre protein metabolism, for example, gene expression for acetylcholine receptor synthesis.

The transillumination possibility of imidazole-osmium postfixed tissue and its consequences for the handling of tissue samples.

Osmium postfixation is established as a routine procedure for transmission electron microscopy (TEM). On the one hand, this routine procedure leads to good results for TEM, but on the other hand results in blackened tissue samples that do not allow examination of any structures within the embedded tissue sample by a light microscope. Equivalent fixation results for TEM are achieved with imidazole-osmium postfixation, and with this postfixation method tissue is not blackened and can be transilluminated with point light sources. This allows easier recognition of histological details within tissue samples and makes it possible to screen embedded samples for appropriate ultrastructural processing. Jejunum is used to demonstrate the method.

On the connection between the T-system and the subsynaptic folds in the motor end plate of amphibians

Using lanthanum as an extracellular marker, the transition between the subsynaptic folds of the motor end plate and the T-system of frog muscle fibres is portrayed for the first time. On the lower segment of the subsynaptic folds of frogs, there are numerous caveolae which can connect with one another to form meandering, branching tubes. The T-system is in contact with these tubes (which run through the sarcoplasm) beneath the motor end plate. In those segments of the end plate with massed sarcoplasm and a cell nucleus, these tubes form networks in close proximity to the cellular organelles. The morphological findings obtained here are compared with findings from mammals. The physiological significance of the transition between the subsynaptic fold and the T-system is discussed.

Early effects of carbachol on the morphology of motor endplates of mammalian skeletal muscle fibers

Long‐term disturbance of the calcium homeostasis of motor endplates (MEPs) causes necrosis of muscle fibers. The onset of morphological changes in response to this disturbance, particularly in relation to the fiber type, is presently unknown. Omohyoid muscles of mice were incubated for 1–30 minutes in 0.1 mM carbachol, an acetylcholine agonist that causes an inward calcium current. In these muscles, the structural changes of the sarcomeres and the MEP sarcoplasm were evaluated at the light‐ and electron‐microscopic level. Predominantly in type I fibers, carbachol incubation resulted in strong contractures of the sarcomeres underlying the MEPs. Owing to these contractures, the usual beret‐like form of the MEP‐associated sarcoplasm was deformed into a mushroom‐like body. Consequently, the squeezed MEPs partially overlapped the adjacent muscle fiber segments. There are no signs of contractures below the MEPs if muscles were incubated in carbachol in calcium‐free Tyrodes solution. Carbachol induced inward calcium current and produced fiber‐type–specific contractures. This finding points to differences in the handling of calcium in MEPs. Possible mechanisms for these fiber‐type–specific differences caused by carbachol‐induced calcium entry are assessed. Muscle Nerve, 2009