CHARACTERIZATION OF A UNIQUE MUSCLE CELL LINE

A clonal cell line derived from a mouse neoplasm is described which shares many properties with smooth muscle. The cells have electrically excitable membranes capable of generating overshooting action potentials, and they contract both spontaneously and with electrical stimulation. They respond to the iontophoretic application of acetylcholine with a depolarizing response, and to norepinephrine with a hyperpolarizing response. Electron microscopy reveals that the cells have a morphology similar in many, but not all, respects to that of smooth muscle cells in vivo. The cells secrete soluble collagen-like molecules in addition to several proteins of undefined function. Finally, there is an increase in the specific activities of creatine phosphokinase and myokinase associated with increased cell density and the cessation of cell division.

The Mechanism of Acute Neuromuscular Weakness Induced by Chloroquine

Chloroquine caused muscle weakness in neuromuscular preparations of both frog and cat in doses as low as those used in clinical practice. Studies of end-plate and action potentials in the muscle fibers and action potentials in single nerve fibers showed that the muscle weakness induced by chloroquine resulted from depression of the excitability of the electrically excitable membranes of the axon and muscle fiber. This led to the decrease of action potentials of the axon resulting in the reduction of transmitter output at the end plate and decreased firing index, as well as to the decrease in the amplitude of action potential of the muscle fiber itself. It was inferred that the mechanism of action of chloroquine was similar to that of local anesthetics.