Bioelectricity from eels

17 Aug 2017. NUS biologists have gained insights on factors affecting electric discharge intensity from the electric eel, Electrophorus electricus.

Electric fishes can generate strong electric organ discharges (EODs) for predation and defense or weak EODs for communication and sensing of their surroundings. One of them, the electric eel, Electrophorus electricus, has the ability to generate both high and low voltage discharges. It has three electric organs (EOs) to produce electricity: the main EO, the Hunter’s EO, and the Sach’s EO. These EOs make up a large part of its body. Prof Alex IP and his students from the Department of Biological Sciences, NUS have cloned and obtained the genetic sequence of certain transporters from the EOs of the electric eel. This information will provide valuable insights into how the electric eel is able to generate electrical discharges for potential bioelectricity applications.

Bioelectricity represents a type of renewable energy. Understanding how EOs generate strong pulses of bioelectricity and elucidating the molecular mechanisms involved are important steps for research in this area. EOs comprise modified muscle cells known as electrocytes. If muscle cells can be modified into electrocytes, they can be designed to power biodegradable electronics, some of which may have important biomedical applications.

Electrophorus electricus has EOD that is powerful enough to stun its prey. The main EO can generate a burst of EOD peaking at 600 V with a current of 2 A within one second for hunting or defense. The Sach’s EO produces low voltage EODs of about 10 V for electro-sensing or electro-communication, while the Hunter’s EO can produce both high and low voltage EODs. How the three EOs generate different types of EODs for various functions is currently an enigma.

The researchers have cloned and sequenced the voltage-gated Na⁺ channel (scn) α-subunit (scna) and β-subunit (scnb) from the three EOs of E. electricus, and evaluated their possible roles in electrogenesis. This is the first time that the full coding sequences of two scna (scn4aa and scn4ab) and three scnb (scn1b, scn2b and scn4b) from E. electricus have been obtained. They found that the scn4aa transcript level was the highest in the main EO and the lowest in the Sach’s EO, denoting its important role in generating high voltage EODs. For scnb, the transcript level of scn4b was much higher than those of scn1b and scn2b in the EOs. Hence, it is unlikely that Scna could function independently to generate EODs as previously suggested. Rather, different combinations of Scn4aa/Scn4ab and various Scnb isoforms in the three EOs may account for the differences in EODs produced.

The researchers are working on understanding the roles of other ion transporters, e.g. Voltage-gated Ca²⁺ channel subunit isoforms, involved in electrogenesis in the EOs of E. electricus. They also intend to extend the research to marine electric fishes to find out if differences exist between EOs of freshwater and marine electric fish species.

Figure shows the absolute quantification (×103 copies of transcript per ng of cDNA) of scn4aa transcripts in the main EO, the Hunter’s EO, the Sach’s EO and the skeletal muscle (SM) of adult E. electricus kept in fresh water. Results represent means ± S.E.M. (N=4). Means not sharing the same letter are significantly different (P<0.05).

Reference

Ching B; Woo JM; Hiong KC; Boo MV; Wong WP; Chew SF; Ip YK*, “Voltage-gated Na+ channel isoforms and their mRNA expression levels and protein abundance in three electric organs and the skeletal muscle of the electric eel Electrophorus electricus” PLOS ONE Volume: 11 Issue: 12 Article Number: e0167589 DOI: 10.1371/journal.pone.0167589 Published: 2016.