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.

NEUROSECRETION OF CRUSTACEAN HYPERGLYCEMIC HORMONE EVOKED BY AXONAL STIMULATION OR ELEVATION OF SALINE K+ CONCENTRATION QUANTIFIED BY A SENSITIVE IMMUNOASSAY METHOD.

A sandwich-type enzyme-linked immunosorbent assay (ELISA) was utilized to quantify crustacean hyperglycemic hormone (as Carcinus maenas equivalents) released by single X-organ­sinus gland systems of the crab Cardisoma carnifex during continuous perifusion. Basal rates of secretion (20­60 pg min-1) were stable for at least 4 h. Electrical stimulation (600 stimuli in 5 min) of the axon tract increased secretion two- to threefold, but only if it resulted in neural activity that was propagated to the terminals of the sinus gland.

Crustacean peptidergic neurons in culture show immediate outgrowth in simple medium.

The survival and outgrowth of neurons in culture has usually required conditioning factors. We now report that crustacean neurons, taken from the peptidergic neurosecretory system of the eyestalk of crabs (Cardisoma carnifex) and lobsters (Panulirus marginatus), show immediate outgrowth, sustained for a week or more, in defined medium as simple as physiological saline with glucose and glutamine. The neurons show peptide hormone immunoreactivity that is prominent at growth cones, exhibit differences in form correlated with their immunoreactivity, release peptides to the medium, and have voltage-dependent currents, including a well-sustained Ca current.

Ultrastructural changes in isolated peptidergic nerve terminals induced by digitonin permeabilization and K+ stimulation in the sinus gland of the crab, Cardisoma carnifex.

The preparation of isolated peptidergic nerve terminals from the sinus gland (a neurohemal organ) of the crab (Cardisoma carnifex) is described. In this species the nerve endings can have diameters up to 30 microns. They release neurosecretory material as judged by the decrease in the volumetric density of granules upon depolarization with potassium.

Ultrastructural changes associated with K+-evoked peptide secretion from a neurohemal organ of the crab, Cardisoma carnifex.

Electron-microscopic comparison of K+-stimulated and unstimulated crab sinus glands reveals significant differences in neurosecretory terminal morphology. Sinus glands exposed to elevated K+ saline for increasing periods of time show increasing numbers of exocytotic release profiles, vacuoles, and multilamellate bodies, and a decrease in the number of microvesicles within 10 micron of release sites. These morphological changes are well correlated with secretion of red-pigment-concentrating hormone, as determined by bioassay of perfusate from the individual preparations.