Facilitation, Augmentation, and Potentiation of Transmitter Release

This chapter discusses facilitation, augmentation, and potentiation of transmitter release. The effect of repetitive stimulation on transmitter release has been studied to look for and characterize the processes in the nerve terminal that affect the transmitter release. During repetitive stimulation of a neuromuscular junction under conditions of low quantal content, end-plate potentials progressively increase in amplitude. This increase is due to an increase in the number of quanta of transmitter released by each nerve impulse. A kinetic analysis of the changes in transmitter release during and following repetitive stimulation suggests that, there are four processes that act to increase transmitter release: first and second components of facilitation that decay with time constants of about 50 and 30 msec, augmentation that decays with a time constant of about 7s, and potentiation that decays with a time constant, which ranges from about 30s to min. These processes are separable on the basis of their kinetic and pharmacological properties. The mechanisms of these processes are not yet known, but some possibilities are briefly discussed in terms of structural, chemical, and statistical factors

[53] Preventing artifacts and reducing errors in single-channel analysis

The power of single-channel analysis techniques has rapidly expanded during the past few years, giving investigators increased ability to identify models and estimate parameters while reducing error and artifacts. At present, however, there is no single best method, as even the most advanced techniques have various limitations which depend on the experimental data and models being examined. Consequently, for the examined models and experimental data, the most critical part of single-channel analysis is to estimate errors and evaluate the ability of the methods used to discriminate among possible gating mechanisms. The magnitudes of the errors and the ability to identify models and estimate parameters depend on the models being examined as well as the experimental conditions and data. Consequently, the evaluation of the errors associated with each method needs to be repeated when the experimental data and examined models change

Calcium-activated potassium channels

Ca 2+-activated K + currents are found in most types of cells. Considerable progress has been made since the development of single channel recording techniques in identifying some of the channels underlying these currents. It is now apparent that there are many types of Ca 2+-activated K + channels, which differ in their conductances and sensitivity to activation by both [Ca 2+] i and voltage. Ca 2+-activated K + channels couple Ca 2+ metabolism and membrane potential to K + flux and membrane excitability. Ca 2+-activated K + channels allow and modulate repetitive firing in some neurons and contribute to regulation of secretion in some endocrine and exocrine cells