Arsenazo III transients and calcium current in a normally non‐spiking neuronal soma of crayfish.

Abstract

SUMMARY1. Arsenazo III was used to investigate Ca2+ transients in the normally non-excitable soma of the motor giant neurones of the crayfish Procambaru8 clarkii.2. Two kinds of regenerative potentials could be obtained depending on membrane potential conditioning: a fast spike after a pre-hyperpolarization to -90 mV and a slow action potential after a pre-depolarization to -50 mV. Only the second of these was accompanied by an Arsenazo III transient.3. In voltage-clamped, somata injected, with tetraethylammonium chloride, an absorbance change could be obtained by pulsing the membrane potential above -44 mV. The relationship between absorbance change and potential peaked between 0 and + 10 mV then fell off to zero at ca. + 150 mV.4. Changes in light absorbance studied using double-pulse protocols suggested that the inactivation of Ca2+ entry was predominantly mediated by the intracellular free Ca2+ concentration.5. External application of 1 mM-CdCl2 abolished both the absorbance changes and the (Ca2+) inward current. The voltage dependence of this current was similar to that of the absorbance change.6. For positive membrane potential the current-voltage relationship showed a voltage-dependent conductance property, the origin of which is discussed.

Crustacean Phasic and Tonic Motor Neurons

“…More detailed descriptions of motor neuron mem- Msghina et al (1998Msghina et al ( , 1999 brane channels have emerged from studies of fast (phasic) flexor neurons, and also from work on swimmeret neurons (Chrachri, 1995). The somata of fast flexor motor neurons usually do not produce action potentials, but nevertheless possess Na and Ca channels which can generate two types of action potential when K channels are partially inactivated, or when Na channel inactivation is alleviated (Czternasty et al, 1984(Czternasty et al, , 1989Roux-Bruxelle et al, 1991;Bruner et al, 1986). In fast flexor motor neuron F3, two types of Ca channel have been described, one resembling P/Q type channels of other organisms, and another less readily characterized Lnenicka, 1995, 1997).…”