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Potential created by electrogenic ionic pumps under conditions of maximum activation in a warm standard ionic medium with K(+) after preincubation in cold potassium-free solution has two components: a higher ouabaine-insensitive "stationary" component, and a lower "regulatory" component sensitive to ouabaine, furosemide, and removal of Cl(-) or Ca(2+) from the medium. Functional heterogeneity of electrogenic ionic pumps is hypothesized implying the existence of two components: "stationary" (not regulated extracellularly) and "regulatory" (controlled and directly related to active Cl(-) transfer).

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.

Three types of miniature excitatory synaptic currents were recorded in the same synaptic region of earthworm muscle cells: monoexponential (tau=1.2 msec) and biexponential (tau(1)=1.2 and tau(2)=8.0 msec). It was hypothesized that earthworm muscle cells contain at least two populations of acetylcholine-sensitive ionic channels, which do not belong to classical nicotinic and muscarinic acetylcholine receptors.

Carbacholine depolarizes Lumbricus terrestris myocyte membrane. Addition of verapamil, tetrodotoxin, removal of K(+), Cl(-), and Ca(2+), and replacement of Ca(2+)with Mn(2+)in the bathing solution did not prevent the carbacholine-induced decrease in resting potential, but in a sodium-free medium carbacholine was ineffective. It was hypothesized that depolarization of the sarcolemma resulting from activation of cholinomimetic-sensitive channel-receptor complex of the Lumbricus terrestris somatic muscle cells is primarily determined by sodium permeability of the membrane.

The miniature excitatory postsynaptic currents (MEPCs) of the muscle cells of the earthworm Lumbricus terrestris were recorded by glass microelectrodes. In a single synaptic zone, three types of MEPC were recorded: a fast singleexponential type that decayed with τ =0.9 ms, a slow single-exponential with τ = 9.2 ms and a two-exponential MEPC with τ = 1.3 and 8.5 ms, respectively. The muscle cells of earthworms contain populations of yet-unidentified ionic channels that might be different from the common nicotinic and muscarinic groups of acetylcholine receptors, since these MEPCs are not sensitive to d-tubocurarine, atropine, benzohexonium or proserine. Alternatively, besides ACh receptors, the membrane may contain receptors for another yet-unidentified excitatory transmitter. [ABSTRACT FROM AUTHOR]