Excitatory effects of cholinergic,adrenergic and glutaminergic agonists on a buccal muscle of Aplysia

The anterior extrinsic protractors in the buccal mass of Aplysia are symmetrical sheets of branching bundles of muscle fibers which form an electrical syncytium. The addition of potassium or cholinergic, adrenergic, and glutaminergic agonists to the sea water bathing medium produces contracture of the muscle. Strychnine and cholinergic or adrenergic antagonists all block contractures produced by cholinergic and adrenergic agonists but not those produced by potassium or glutamate. Iontophoretic application through microelectrodes of acetylcholine or dopamine anywhere on the muscle surface produced a graded depolarization of the membrane. By contrast, glutamate produces depolarization only at discrete membrane sites. Endogeneous contractions often appeared spontaneously or could be induced by drug exposure. ATP inhibits endogeneous contractions.     

Dual effect of L-glutamate on excitatory postjunctional membranes of crayfish muscle

Iontophoretically applied glutamate produces different excitatory postjunctional permeability changes on separate muscle fibers in a single crayfish muslce. At junctions on some fibers glutamate appears to increase the conductance to both sodium and potassium whereas at others its effect is primarily on the sodium conductance. These results obtained by studying the reversal potential for the extracellularly recorded glutamate potential under conditions of varied extracellular sodium and potassium concentrations.     

Electrical activity in adenohypophyseal cells and effects of hypophyseotropic substances

Normal endocrine cells isolated from adenohypophyses of the rat, lizard, and fish, and maintained in short-term culture, produce action potentials spontaneously or in response to depolarizing current pulses or stimulant hypophyseotropic substances. Thyrotropin-releasing hormone elicited action potentials in a fraction of a mixed population of rat pars distalis cells. Dopamine, which inhibits basal secretion from rat melanotrophs and teleostean prolactin cells, inhibited action potential discharge in both these cell types. 5-Hydroxytryptamine, which stimulates secretion from lizard pars intermedia cells, stimulated action potentials in these cells. gamma-Aminobutyric acid, recently found in nerves to the rat pars intermedia and shown to have both stimulant and inhibitory effects on secretion, depolarized rat melanotrophs. The effect involved an increase in Cl conductance, which could be blocked by bicuculline and potentiated by diazepam. A Ca component that indicates inward Ca flux was present in the action potentials in each of the cell types examined, although its contribution varied with species and gland region. Electrical activity may therefore participate in secretory control in adenohypophyseal cells. Attention is drawn to some unexpected electrical responses to agents that are likely to be used in attempts to examine the correlation between the electrical events and secretion.     

The role of laboratory-scale bioreactors at the semi-continuous and continuous microbiological and biotechnological processes

Applied Microbiology and Biotechnology - Laboratory-scale bioreactors represent an important part of microbiological, biotechnological, and biochemical researches. The small volume bioreactors...