Segregation of leech neurones by the effect of sparteine on action potential duration.

Abstract

SUMMARY1. Sparteine (SPT) and 3-or 4-aminopyridine, were applied to leech segmental ganglia and the electrophysiological responses ofthe Retzius (R) and sensory neurones responding to pressure (P), touch (T), and noxious (N) stimuli analysed.2. SPT 0*05-0*5 mm when presented via the bath to the whole ganglion prolonged the action potentials of these neurones to characteristically different degrees; the cells were clearly segregated in the order R > N > P > T at 0 5 mm, regardless of exposure time.3. The plateau of the prolonged action potentials in the R and N cells was sustained by either Ca or Sr and was blocked by Mn, in normal or Na-free Ringer. These responses were similar to those seen in the same cell types with TEA under the same condition.4. The SPT prolongation of action potentials was favoured by alkalinization of the Ringer solution. This implies that the drug acted in its uncharged form. SPT was ineffective when applied by pressure into the somata of these four neurones. This may be because SPT was charged at the intracellular pH or because it acted at some external membrane site.5. The aminopyridines when applied in the bath had no effect on the repolarization of these four neurones.6. These results suggest that TEA and SPT probably act on repolarization by similar mechanisms. The parameter of membrane function principally affected is probably a K current which contributes to repolarization to different degrees in the four cells and which may be activated by Ca.

Inhibition of Ca2+ conductance in identified leech neurons by benzodiazepines.

“…2A), and both Mn2' and BZs in micromolar concentrations completely blocked the Sr2' potential. Furthermore, both Mn2+ and BZs caused a marked decrease in the size of the undershoot of the Na+-dependent action potential, presumably due to a decrease in the contribution of Ca2+-dependent K+ conductance, resulting from diminished Ca2+ entry (18,22). The close similarity of BZ and Mn2+ actions on leech neurons is consistent with the view that the BZs inhibit the same Ca2+ conductance as does M2+.…”

“…8). In the present study, we used Sr2' as the current carrier because it produced the most stable recording conditions and because there is evidence that Sr2' in leech neurons may be less effective than Ca2+ in activating Ca2+-dependent K+ conductances, 9KCa (18,19).…”

Voltage clamp characterization of a calcium-dependent chloride conductance in a putative invertebrate motoneuron

“…The leeches of this species, which were the generous gift of Drs. The procedures for dissection, current clamp recording, and for perfusion of the experimental chamber were similar to those described in previous reports (Kleinhaus 1976(Kleinhaus , 1980Johansen and Kleinhaus 1986b). Muller and E. McGlade-McCulloh (University of Miami) and of Dr. E.M. Burreson (Virginia Institute of Marine Science), were maintained at room temperature.…”

Reflections on Bill 11: The Domestic Violence and Stalking Amendment Act

“…The Commission's report can be seen as an aggressive attempt to reaffirm the monopoly of a reformed state law with respect to questions of guilt or innocence or what Macdonald identifies as the orthodoxy of state law. 147 In contrast, a critical legal pluralist approach would be neither surprised nor offended by alternative legal conclusions of the sort that Wheat Kings draws.…”