Arsenazo III transients and calcium current in a normally non-spiking neuronal soma of crayfish.
Arsenazo III was used to investigate Ca2+ transients in the normally non-excitable soma of the motor giant neurones of the crayfish Procambarus clarkii. 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. 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. 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. 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. For positive membrane potential the current-voltage relationship showed a voltage-dependent conductance property, the origin of which is discussed.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001150:Arsenazo III / Q000494:pharmacology*; D003400:Astacoidea; D001391:Azo Compounds / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000502:physiology
D001391:Azo Compounds; D007473:Ion Channels; D001150:Arsenazo III; D002118:Calcium