Regulation of calcium currents and secretion by magnesium in crustacean peptidergic neurons.
The effect of varying the external Mg2+ concentration on Ca2+ currents through voltage-operated Ca2+ channels has been examined with the patch-clamp technique in acutely isolated neuronal somata from the X-organ-sinus gland (XOSG) of the crab, Cardisoma carnifex. Neurons from this neurosecretory system were selected for morphology associated with crustacean hyperglycemic hormone (CHH) content. In parallel, the effects of Mg2+ concentration on K(+)-evoked secretion of CHH from isolated, intact XOSGs have been assayed by ELISA. At physiological Ca2+ levels the high-voltage-activated Ca2+ currents were attenuated with increasing Mg2+ concentration, with 50% inhibition at approximately 75 mM. Mg2+ block was voltage-dependent, relief from block occurring with increasing depolarization. Thus, in 24 mM Mg2+ inhibition of the Ca2+ current was approximately 55% at -10 mV. Secretion of CHH varied almost linearly with the log of Mg2+ concentration; in 2.4 mM Mg2+ it was double that in 24 mM Mg2+ and almost completely inhibited in 100 mM. Thus, Mg2+ produces a parallel inhibition of Ca2+ currents and CHH secretion and may play a role as a physiological modulator of neuronal activity and secretion in the XOSG of these crabs.
Richmond
J E
JE
Department of Biology, College of Science, Utah State University, Logan 84322-5305, USA.
Sher
E
E
Keller
R
R
Haylett
B
B
Reichwein
B
B
Cooke
I M
IM
D000818:Animals; D060829:Arthropod Proteins; D003386:Brachyura; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D004553:Electric Conductivity; D007447:Invertebrate Hormones; D008274:Magnesium / Q000494:pharmacology*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009490:Neurosecretory Systems / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques
D060829:Arthropod Proteins; D015220:Calcium Channels; D007447:Invertebrate Hormones; D009419:Nerve Tissue Proteins; C015947:hyperglycemic hormone, crustacean; D008274:Magnesium