Characterization of the Ca2+ current in isolated terminals of crustacean peptidergic neurons.
Ca2+ currents (ICa) were recorded from the neurosecretory terminals of the crab X-organ-sinus gland under voltage-clamp conditions. ICa was detectable at command potentials above -40mV, with maximum currents at approximately +20mV. No differences were observed between current-voltage (I/V) relationships from holding potentials of -50 or -90mV, indicating that there were no low-voltage-activated Ca2+ channels present in the terminals. The decay of ICa was best fitted with a single exponential, the extent of inactivation over 50 ms averaging 53%. The rate of decay of ICa 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 ICa at +20mV was tested. ICa declined with increasing prepulse depolarization up to +20mV 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 ICa decay. ICa was insensitive to nifedipine at a concentration of 1 mumol l-1. Pretreatment of the isolated sinus gland containing the intact terminals with a combination of omega-conotoxin (omega-Ctx) GVIA, omega-Ctx MVIIC and omega-agatoxin IVA had no effect on the levels of K+-induced peptide release.
Richmond
J E
JE
Békésy Laboratory of Neurobiology, University of Hawaii, Honolulu 96822, USA. janet@cc.usu.edu
Penner
R
R
Keller
R
R
Cooke
I M
IM
D000818:Animals; D060829:Arthropod Proteins; D001464:Barium / Q000494:pharmacology; D003386:Brachyura / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D007447:Invertebrate Hormones; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000502:physiology*; D009490:Neurosecretory Systems / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D013324:Strontium / Q000494:pharmacology
D060829:Arthropod Proteins; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002614:Chelating Agents; D007447:Invertebrate Hormones; D009419:Nerve Tissue Proteins; C015947:hyperglycemic hormone, crustacean; D001464:Barium; D004533:Egtazic Acid; D009543:Nifedipine; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D013324:Strontium