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.

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.