Membrane Responses Evoked By Organic Buffers In Identified Leech Neurones Available to Purchase

Using single-electrode current-clamp and two-electrode voltage-clamp, different identified neurones of the leech (Hirudo medicinalis L.) were shown to hyperpolarize, or to exhibit outward currents (usually >2 nA), during bath application of the organic buffers Mops, Pipes and Mes (10 mmol l⁻¹). Tris and Hepes had little or no effect on the membrane properties of neurones when they were added to a bathing saline buffered by CO₂–HCO₃⁻ at a constant pH of 7.4.

Outward currents evoked by buffers obtained from two suppliers, Roth and Sigma, were not significantly different, except in the case of Pipes. Steady-state currents evoked by Pipes supplied by Roth were eightfold larger than steady-state currents evoked by Pipes from Sigma. A transient current peak always present in responses evoked by Pipes from Roth was never present in responses evoked by Pipes from Sigma.

Outward currents evoked by buffers were due to a conductance increase and appeared to be carried by Cl⁻.

In low-Cl⁻ saline, hyperpolarizations evoked by Mops in Retzius cells were reduced. When Cl⁻ was injected into heart motor neurones, the hyperpolarizations evoked by Mops reversed. Tetraethylammonium (TEA⁺) injected into heart interneurones did not block Mops-evoked hyperpolarizations.

Mops-evoked outward currents in Retzius cells were partially blocked by d-tubocurarine and bicuculline methiodide, and the latter also partially blocked Mops-evoked hyperpolarizations in HE cells. Since d-tubocurarine partially blocked acetylcholine-evoked Cl⁻ currents in Retzius cells and bicuculline methiodide partially blocked carbachol-evoked hyperpolarizations in HE cells, Mops appears to act on the cholinergic receptors of these neurones by mediating a Cl⁻ conductance.