Characterization of the Ca²⁺ current in isolated terminals of crustacean peptidergic neurons

Richmond, Penner, Keller and Cooke
J. Exp. Biol. 199: 2053-2059 (1996)

Summary

Ca²⁺ currents (I_Ca) were recorded from the neurosecretory terminals of the crab X-organ-sinus gland under voltage-clamp conditions.  I_Ca was detectable at command potentials above -40 mV, with maximum currents at approximately +20 mV.  No differences were observed between current-voltage (I/V) relationships from holding potentials of -50 or -90 mV, indicating that there were no low-voltage-activated Ca²⁺ channels present in the terminals.  The decay of I_Ca was best fitted with a single exponential, the extent of inactivation over 50 ms averaging 53 %.  The rate of decay of I_Ca was reduced by the substitution of Ca²⁺ with Sr²⁺ in the external solution and was eliminated by substitution with Ba²⁺.

The effect of varying prepulse potential on the amplitude of I_Ca at +20 mV was tested.  I_Ca declined with increasing prepulse depolarization up to +20 mV and then showed partial recovery at more depolarized prepulse potentials.  Inactivation curves in solutions containing Sr²⁺ and Ba²⁺ showed much less current-dependent inactivation.  Removing Ca²⁺ chelators from the internal solution significantly increased I_Ca decay.  I_Ca was insensitive to nifedipine at a concentration of 1 µmol I^-1.  Pretreatment of the isolated sinus gland containing the intact terminals with a combination of ω-conotoxin (ω-Ctx) GVIA, ω-Ctx MVIIC and ω-agatoxin IVA had no effect on the levels of K⁺-induced peptide release.

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