Neuromuscular transmission of pectoral fin muscles of the goldfish Carassius auratus.

The electrical properties and neuromuscular transmission of white and red fibers of pectoral fin muscles of the goldfish Carassius auratus were studied using an intracellular recording technique. The pectoral fin muscles consist mainly of white and red fibers. Almost all of white fibers elicited action potentials with overshoot by direct stimulation, but graded responses appeared in the red fibers. However, overshooting action potentials were often recorded from the red fibers in saline containing 20 microM tetraethylammonium (TEA) chloride. In response to single nerve stimulations, excitatory (EJPs) and inhibitory junction potentials (IJPs) were obtained from both white and red fibers in common. Both EJPs and IJPs were blocked completely or partially by d-tubocurarine, a nicotinic acetylcholine (ACh) receptor antagonist. Nicotine, a nicotinic ACh receptor agonist, and oxotremorine, a muscarinic ACh receptor agonist, depolarized both fiber types. The results suggest that white and red fibers receive double innervation from excitatory and inhibitory nerves, and have nicotinic and muscarinic ACh receptors. In the resting muscle, miniature excitatory junction potentials were generated spontaneously in both white and red fibers. Occasionally, miniature inhibitory junction potentials were recorded from the red fibers. The results indicate that the release of both excitatory and inhibitory transmitters is quantal in nature.