Frequency-dependent depression of ganglionic transmission by propranolol and diltiazem in the superior cervical ganglion of the guinea-pig

Abstract

1 Effects of propranolol and diltiazem on ganglionic transmission in the superior cervical ganglion of the guinea-pig were investigated with intracellular recording techniques. 2 Propranolol and diltiazem (5 X 10(-6)-10(-5) M) induced a transmission failure in the ganglion upon preganglionic nerve stimulation at high frequency (25-30 Hz) without affecting action potentials induced by direct stimulation of the soma membrane, or potentials induced by iontophoretically applied acetylecholine. 3 The results suggest that propranolol and diltiazem may act on preganglionic nerve terminals to inhibit Ca2+ influx in a frequency-dependent manner. These agents may depress excess sympathetic activity without much affecting normal ganglionic transmission.