Calcium currents modulated by adrenergic receptors in sympathetic neurons.
The superior cervical sympathetic ganglion is currently being used as a model neuronal system for the study of Ca2+-dependent processes in the mammalian nervous system. We have characterized a regenerative calcium conductance in postganglionic neurons. This Ca2+ current contributes to the shoulder of the action potential. In addition, Ca2+ influx during the spike activates a K+ conductance, which generates a hyperpolarizing afterpotential. These Ca2+-dependent potentials are antagonized by catecholamines. Pharmacologic studies suggest that alpha 2-adrenergic receptors inhibit the regenerative voltage-dependent Ca2+ influx that occurs during the action potential. Alpha-adrenergic agonists were also found to reduce the depression of the compound action potential following a train of preganglionic stimuli. We hypothesize that alpha 2-receptors function primarily to antagonize Ca2+ influx and thereby exert significant control over neuronal excitability and release of neurotransmitters.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002395:Catecholamines / Q000494:pharmacology; D005728:Ganglia, Sympathetic / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D002395:Catecholamines; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D013779:Tetrodotoxin; D002118:Calcium; D009638:Norepinephrine; D010646:Phentolamine