Calcium ions and their relation to sympathetic ganglionic transmission and to cyclic AMP levels in isolated superior cervical ganglion of the rat in vitro.

The rat superior cervical ganglion was investigated $\text{in vitro}$ by means of extracellularly recorded compound action potentials and of cyclic AMP content in relation to Ca²⁺-concentrations in the extracellular fluid. Threshold concentrations for the appearance of the potentials were lower than 1 mM. Raising the Ca²⁺-content in the Krebs solution above 40 mM led to an increase of the slow excitatory negative potential and to the appearance of the slow inhibitory positive wave, while the fast excitatory compound action potential disappeared. This effect was calcium-specific. On the other hand, cyclic AMP accumulation in the ganglion seems to be calcium-independent. While high Ca²⁺-concentrations (60 mM) in the medium led to a significant decrease of the cyclic AMP content, neurotransmitter-induced cyclic AMP accumulation occurred regardless from varying the extracellular calcium content. High external Ca²⁺ antagonized the ability of the β-adrenergic blocker propranolol in preventing isoproterenol-induced cyclic AMP accumulation to some extent. It was concluded that calcium ions are necessary for the appearance of fast and slow postganglionic compound action potentials in the ganglion. These events seemed to be independent from drug-induced changes in the ganglionic cyclic AMP content.