The Effect of CO2, Intracellular pH and Extracellular pH on Mechanosensory Proprioceptor Responses in Crayfish and Crab

Abstract

Proprioceptive neurons monitor the movements of limbs and joints to transduce the movements into electrical signals. These neurons function similarly in species from arthropods to humans. These neurons can be compromised in disease states and in adverse environmental conditions such as with changes in external and internal pH. We used two model preparations (the crayfish muscle receptor organ and a chordotonal organ in the limb of a crab) to characterize the responses of these proprioceptors to external and internal pH changes as well as raised CO2. The results demonstrate the proprioceptive organs are not highly sensitive to changes in extracellular pH, when reduced to 5.0 from 7.4. However, if intracellular pH is decreased by exposure to propionic acid or saline containing CO2, there is a rapid decrease in firing rate in response to joint movements. The responses recover quickly upon reintroduction of normal pH (7.4) or saline not tainted with CO2. These basic understandings may help to address the mechanistic properties of mechanosensitive receptors in other organisms, such as muscle spindles in skeletal muscles of mammals and tactile as well as pressure (i.e., blood pressure) sensory receptors. KEYWORDS: Proprioception; Sensory; Invertebrate; Carbon Dioxide; Protons; Mechanosensory; Intracellular pH; Extracellular pH

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

“…The SACs within the sensory endings of the crustacean chordotonal organs are not likely a PIZEO 2 subtype since this subtype is a Ca 2+ permeant type in mammals [23]. Likewise, earlier pharmacology studies do not allude to these crustacean SACs as a PIEZO1 or DEG/ENaCs subtype [24][25][26]. The genomic or protein sequence for these SACs in crustaceans remains to be determined.…”

“…To date, the subtype of SACs in chordotonal organs in crustaceans has not been fully identified. It appears they are not PIEZO1 nor DEG/ENaCs (Degenerin/epithelial sodium channel) subtype from previous studies as examined with low pH (pH5), ruthenium red, amiloride and Gd 3+ [24][25][26]. Only Gd 3+ provided evidence of reduced activity and was reversible but it is not a specific blocker in types of SACs [26].…”

“…The arrangement the crab chordotonal organ enables for the exploration of the direct effects of agents on the sensory endings, without the effects on muscle fibers, as well as axon excitability [27,28]. Given there is still an active interest in how [Ca 2+ ] o influences the function of nerves as well as understanding the function of SACs, in the vast variety of SAC subtypes, among organisms [29], the crab leg proprioceptive neurons serve as a viable model for such investigations [24][25][26][27][28]30].…”

Harnessing Mechanical Forces for Cancer Treatment

“…In vitro on non-cancerous cells, sensory cells [50], Piezo-expressing HE293T cells [51] TRPV4 GSK2798745…”

“…Several antagonists have been developed in recent years [88,89], of which GSK2798745 is the first TRPV4 blocker in clinical trial studies and was tolerated by patients in the early phases. [50] YAP/TAZ are transcription coactivators activated by mechanical stress and other types of signals, which act as signal transducers to the nucleus. The constitutive activation of YAP/TAZ was responsible for the uncontrolled growth of tumors.…”