The Effect of Calcium Ions on Mechanosensation and Neuronal Activity in Proprioceptive Neurons

Abstract

Proprioception of all animals is important in being able to have coordinated locomotion. Stretch activated ion channels (SACs) transduce the mechanical force into electrical signals in the proprioceptive sensory endings. The types of SACs vary among sensory neurons in animals as defined by pharmacological, physiological and molecular identification. The chordotonal organs within insects and crustaceans offer a unique ability to investigate proprioceptive function. The effects of the extracellular environment on neuronal activity, as well as the function of associated SACs are easily accessible and viable in minimal saline for ease in experimentation. The effect of extracellular [Ca2+] on membrane properties which affect voltage-sensitivity of ion channels, threshold of action potentials and SACs can be readily addressed in the chordotonal organ in crab limbs. It is of interest to understand how low extracellular [Ca2+] enhances neural activity considering the SACs in the sensory endings could possibly be Ca2+ channels and that all neural activity is blocked with Mn2+. It is suggested that axonal excitability might be affected independent from the SAC activity due to potential presence of calcium activated potassium channels (K(Ca)) and the ability of Ca2+ to block voltage gated Na+ channels in the axons. Separating the role of Ca2+ on the function of the SACs and the excitability of the axons in the nerves associated with chordotonal organs is addressed. These experiments may aid in understanding the mechanisms of neuronal hyperexcitability during hypocalcemia within mammals.

The Effects of Zinc on Proprioceptive Sensory Function and Nerve Conduction

“…At present, SACs in the crab PD organ are believed to be of the DEG/ENaCs subtype, making them permeable to Na + [38]. Previous investigations into bathing solutions absent added Ca 2+ still allowed the PD organ to respond to joint movements [28]. Additionally, as previously mentioned, the PD organ was used to screen newly described pharmacological compounds (YODA 1, JEDI 2, OB 1 and DOOKU), SACs of the PIEZO 1 subtype; these were found to have no effect on the activity of the crab PD organ [31].…”

“…The general procedures followed are similar to those previously described in detail [28,29,33] and in a video format [37].…”

“…Generally, information is relayed to an animal's central nervous system using both dynamic and static displacement-sensitive neurons [22][23][24][25][26][27]. Large crabs, like the common blue crab in question (Callinectes sapidus) or the Dungeness crab (Cancer magister), feature a nerve of approximately ten to fifteen centimeters, located from the most distant chordotonal organ, the PD organ (the propodite-dactylopodite organ), to the base of the thorax; this allows for the easy examination of electrical conduction along the nerve, as well as an investigation into how exposing the nerve to different baths (and, within the baths, different agents) could affect this conduction [28,29].…”

“…It is not yet known what types of SACs are located within the sensory endings of these chordotonal organs, as these have yet to be fully described via either pharmacological profile or mechano-electrical transduction properties. However, the subtype present in the crab chordotonal organs seems to maintain function without a need for Ca 2+ in the bathing environment [28]. These channels are not affected by compounds that traditionally affect SACs, to the point that traditional antagonists and agonists-such as amiloride, ruthenium red, and/or streptomycin-do not function in their usual manners [30,31].…”

Marine invertebrates and noise

“…Chordotonal organs which are associated with flexible articulations of the appendages, are common among crustaceans (Bush and Laverack, 1982;Cooper, 2008;Atkins et al, 2021) (Figure 7). The oscillations of the water column stimulate the chordotonal sensory cells sited in the appendages.…”