Effects of tetraethylammonium chloride on sympathetic neuromuscular transmission in saphenous artery of young rabbits.

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Abstract
Excitatory junction potentials [e.j.p.] and electrotonic potentials were recorded from the smooth muscle of the rabbit saphenous artery using intracellular electrodes. Tetraethylammonium chloride (TEA) in concentrations greater than 2.5 mM caused depolarization. Concentrations greater than 5 mM caused spontaneous electrical activity in the form of e.j.p. and all-or-nothing action potentials which were associated with spontaneous mechanical activity. Concentrations of TEA less than 2.5 mM did not alter the resting potential or the passive membrane properties of the smooth muscle over a range of .+-. 15 mV. The following effects were observed in 2.0 mM-TEA: The minimum stimulus strength required for the initiation of an e.j.p. fell by 3-5-fold. Single stimuli that elicited only a small e.j.p. in normal solution evoked an all-or-nothing action potential of up to 70 mV amplitude. E.j.p. were recorded at distances of up to 13 mm from the perivascular stimulating electrode, 6 mm more than in normal solutions. The duration of the e.j.p. was prolonged. TEA may act to increase the amount of transmitter released per axon, to increase the duration of release and to cause an increased invasion throughout the autonomic ground plexus by nerve impulses. In normal solution, in vitro, the action potential may not propagate throughout the whole length of the terminal axon and its many branches due to failure of conduction at 1 or more points along the terminal portion of the axon.