Effect of GABAergic and adrenergic agents on activity of Na+/K+ pump and Cl(-)-cotransport in somatic muscle cells of earthworm Lumbricus Terrestris.

GABA, baclofen, epinephrine, and norepinephrine hyperpolarized the membrane of earthworm somatic cells. This effect was prevented by furosemide, removal of Cl- from the medium, or activation of Na+/K+ pump by 3-fold increase external potassium concentration. It was hypothesized that GABA, baclofen, epinephrine, and norepinephrine stimulate Na+/K+ transport via specific receptor inputs, but their effect on resting potential can be realized only under conditions of working Cl- symport.

Effects of cholinergic receptor agonists and antagonists on miniature stimulatory postsynaptic ionic currents in somatic muscle cells of lumbricus terrestris.

Miniature stimulating postsynaptic currents of Lumbricus terrestris somatic muscle cells were recorded. Atropine, d-tubocurarin, alpha-bungarotoxin, carbacholine, and proserin did not modify the amplitude and temporal parameters of miniature stimulatory postsynaptic currents, while carbacholine and nicotine depolarized the muscle membrane. Presumably, Lumbricus terrestris muscle cells contain acetylcholine-sensitive channel-receptor complexes not belonging to classical nicotinic or muscarinic acetylcholine receptors.

Mechanisms of hyperpolarizing effect of GABA on resting potential of the Lumbricus terrestris muscular wall somatic cells.

GABA, baclofen, isoguvacine increase, and cis-4-aminocrotonic acid does not modify resting membrane potential of muscle cells. Bicuculline, phaclofen, N-ethylmaleimide, chlorpromazine, verapamil, and removal of Ca2+ from bathing solution abolished the effect of baclofen, while U73122 and D609 were ineffective in this respect. The authors conclude that the Lumbricus terrestris muscle cells contain GABAergic structures similar to a- and b-receptors.

Effects of some transmitters on resting membrane potential of somatic cell in Lumbricus terrestris muscle wall.

Serotonin, glutamate, glycine, ATP, and muscarine had no effect on resting membrane potential of muscle cell in earthworm Lumbricus terrestris. Nicotine depolarizes and GABA hyperpolarizes the muscle membrane. Removal of K(+), Cl(-) and addition of ouabaine and strychnine to the solution abolished the effect of GABA.

Calcium mechanism of norepinephrine activation of ionic pump in somatic cells of lumbricus terrestris earthworm muscle wall.

Blockade of norepinephrine-induced hyperpolarization in earthworm muscle cells was observed in a calcium-free medium, after substitution of Ca(2+)with Mn(2+), and in the presence of verapamil or chlorpromazine to the incubation saline. Changes in Ca(2+)concentration in the saline and addition of caffeine had no effect on the resting potential of muscle cells. It was hypothesized that signal transduction from norepinephrine-activated membrane adrenoceptors to the ionic pump in earthworm muscle cells depends on influx of extracellular Ca(2+)and subsequent involvement of Ca(2+)-accepting proteins similar to calmodulin in vertebrates.

Effects of norepinephrine and epinephrine on resting membrane potential in body wall muscle cells of Lumbricus terrestris earthworm.

Norepinephrine and to a lesser extent epinephrine increased the resting membrane potential of earthworm body wall muscle cells. Ouabain, phentolamine, propranolol, and replacement of Ca(2+) with Mg(2+) in the incubation medium abolished this effect. External 3'5'-cAMP in high concentration, dibutyryl cAMP, and dibutyryl cGMP did not induced hyperpolarization of muscle cell membranes.

Effect of cholinergic agonists on resting membrane potential of earthworm body wall muscle cells.

Carbachol in a concentration of 5x10(-8) mol/liter does not hyperpolarize, and in a concentration of 5x10(-6) mol/liter depolarizes the membrane of somatic muscle cell in earthworm. d-tubocurarine, alpha-bungarotoxin, atropine, and hexamethonium added to the incubation medium did not abolish the carbachol-induced decrease in resting membrane potential. Each of these drugs alone had no effect on resting membrane potential in muscle cells.