Biomaterial Database

Membrane excitability and secretion from peptidergic nerve terminals. 1998

J L Branchaw, and S F Hsu, and M B Jackson

Department of Physiology, University of Wisconsin-Madison 53202, USA.

1. Thin slices of the posterior pituitary can be used as a preparation for the study of biophysical mechanisms underlying neuropeptide secretion. Patch-clamp techniques in this preparation have revealed the properties of ion channels that control the excitability of the nerve terminal membrane and have clarified the relation between Ca2+ and exocytosis. 2. Repetitive electrical activity at high frequencies broadens action potentials to allow more Ca2+ entry and thus enhance exocytosis. Action potential broadening results from the inactivation of a voltage-dependent K+ channel. 3. When repetitive electrical activity is sustained, secretion is depressed. This depression can be attributed in part to action potential failure caused by the opening of a Ca(2+)-activated K+ channel. This channel can be modulated by protein kinases, phosphatases, and G-proteins. 4. The inhibitory neurotransmitter GABA activates a GABAA receptor in the nerve terminal membrane. The gating of the associated Cl- channel depolarizes the membrane slightly to inactivate voltage-gated Na+ channels and block action potential propagation. 5. The response of the nerve terminal GABAA receptor is enhanced by neuroactive steroids and this can potentiate the inhibition of neurosecretion by GABA. The action of neurosteroids at this site could play a role in changes in neuropeptide secretion associated with reproductive transitions. 6. Ca2+ channels in the nerve terminal membrane are inactivated by sustained depolarization and by trains of brief pulses. Ca2+ entry promotes Ca2+ channel inactivation during trains by inhibiting the recovery of Ca2+ channels from inactivation. The inactivation of Ca2+ channels can play a role in defining the optimal frequency and train duration for evoking neuropeptide secretion. 7. Measurements of membrane capacitance in peptidergic nerve terminals have revealed rapid exocytosis and endocytosis evoked by Ca2+ entry through voltage-gated Ca2+ channels. Exocytosis is too rapid to account for the delays in neuropeptide secretion evoked by trains of action potentials. Endocytosis sets in rapidly after exocytosis with a time course comparable to that of the rapid endocytosis observed in nerve terminals at rapid synapses. Our results support the finding in rapid synaptic nerve terminals that endocytosis is inhibited by intracellular Ca2+. Multiple pools of vesicles were revealed, and these pools may reflect different stages in the mobilization and release of neuropeptide.

UI	MeSH Term	Description	Entries
D009479	Neuropeptides	Peptides released by NEURONS as intercellular messengers. Many neuropeptides are also hormones released by non-neuronal cells.	Neuropeptide
D010904	Pituitary Gland, Posterior	Neural tissue of the pituitary gland, also known as the neurohypophysis. It consists of the distal AXONS of neurons that produce VASOPRESSIN and OXYTOCIN in the SUPRAOPTIC NUCLEUS and the PARAVENTRICULAR NUCLEUS. These axons travel down through the MEDIAN EMINENCE, the hypothalamic infundibulum of the PITUITARY STALK, to the posterior lobe of the pituitary gland.	Neurohypophysis,Infundibular Process,Lobus Nervosus,Neural Lobe,Pars Nervosa of Pituitary,Posterior Lobe of Pituitary,Gland, Posterior Pituitary,Infundibular Processes,Lobe, Neural,Lobes, Neural,Nervosus, Lobus,Neural Lobes,Pituitary Pars Nervosa,Pituitary Posterior Lobe,Posterior Pituitary Gland,Posterior Pituitary Glands,Process, Infundibular,Processes, Infundibular
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000200	Action Potentials	Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.	Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D017729	Presynaptic Terminals	The distal terminations of axons which are specialized for the release of neurotransmitters. Also included are varicosities along the course of axons which have similar specializations and also release transmitters. Presynaptic terminals in both the central and peripheral nervous systems are included.	Axon Terminals,Nerve Endings, Presynaptic,Synaptic Boutons,Synaptic Terminals,Axon Terminal,Bouton, Synaptic,Boutons, Synaptic,Ending, Presynaptic Nerve,Endings, Presynaptic Nerve,Nerve Ending, Presynaptic,Presynaptic Nerve Ending,Presynaptic Nerve Endings,Presynaptic Terminal,Synaptic Bouton,Synaptic Terminal,Terminal, Axon,Terminal, Presynaptic,Terminal, Synaptic,Terminals, Axon,Terminals, Presynaptic,Terminals, Synaptic
D018408	Patch-Clamp Techniques	An electrophysiologic technique for studying cells, cell membranes, and occasionally isolated organelles. All patch-clamp methods rely on a very high-resistance seal between a micropipette and a membrane; the seal is usually attained by gentle suction. The four most common variants include on-cell patch, inside-out patch, outside-out patch, and whole-cell clamp. Patch-clamp methods are commonly used to voltage clamp, that is control the voltage across the membrane and measure current flow, but current-clamp methods, in which the current is controlled and the voltage is measured, are also used.	Patch Clamp Technique,Patch-Clamp Technic,Patch-Clamp Technique,Voltage-Clamp Technic,Voltage-Clamp Technique,Voltage-Clamp Techniques,Whole-Cell Recording,Patch-Clamp Technics,Voltage-Clamp Technics,Clamp Technique, Patch,Clamp Techniques, Patch,Patch Clamp Technic,Patch Clamp Technics,Patch Clamp Techniques,Recording, Whole-Cell,Recordings, Whole-Cell,Technic, Patch-Clamp,Technic, Voltage-Clamp,Technics, Patch-Clamp,Technics, Voltage-Clamp,Technique, Patch Clamp,Technique, Patch-Clamp,Technique, Voltage-Clamp,Techniques, Patch Clamp,Techniques, Patch-Clamp,Techniques, Voltage-Clamp,Voltage Clamp Technic,Voltage Clamp Technics,Voltage Clamp Technique,Voltage Clamp Techniques,Whole Cell Recording,Whole-Cell Recordings