Responses of the rat superior cervical ganglion in vitro to isoprenaline and bethanechol

Abstract

The effects of isoprenaline were studied in isolated rat superior cervical ganglia. Intracellularly recorded excitatory postsynaptic potentials were depressed by isoprenaline in concentrations of 10(-5) to 10(-4)M. In 13 out of 17 cells, isoprenaline caused ganglionic hyperpolarization (mean, 4mV). Changes in the amplitude and contour of antidromic action potentials caused by isoprenaline could be accounted for by the increased membrane potential. A slight increase in membrane input resistance from 44--50.2 megohms (mean values) occurred in about half of the cells. Activation of an ion pump by isoprenaline was suggested by the finding that the hyperpolarization did not occur when the bathing solution contained ouabain (10(-5)M) or lacked Na+ or K+. Characterization of the isoprenaline effects by the use of alpha and beta adrenergic blocking drugs was not possible because of the direct depressant effects of the antagonists. The muscarinic agonist bethanechol (2.5 X 10(-5) to 2.5 X 10(-4)M) caused ganglionic depolarization and increased input membrane resistance (42--52 megohms) during depolarization in each of the cells tested. The ganglionic responses to bethanechol were prevented by atropine.