Electric catfish hearts are not immune to electric bolts

Abstract

Electricity is at once the heart's best friend and fiercest foe. The heart coordinates its own rhythmic beats with repetitive gentle electrical pulses and a sudden jolt of electricity can shock a stopped heart back into action. However, an accidental electric bolt can trigger irregular heartbeats and even fatal heart attacks; electric shocks are generally best avoided. So, how do the hearts of electric catfish (Malapterurus beninensis) that stun prey with 300 V discharges protect the delicate organ? Having previously discovered that the muscles of the extraordinary fish are somehow immune to their own violent electrical discharges, Georg Welzel and Stefan Schuster from the University of Bayreuth, Germany, wanted to know how vulnerable the catfish heart is to powerful electric currents.The duo removed the still-beating organ from a catfish and placed it in liquid laced with sugar and salts to keep the organ alive as they recorded the heart's ECG to find out whether the resilient fish had somehow modified the electrical impulses that regulate the heartbeat to withstand life-threatening shocks. However, when the pair compared the electric catfish's ECG to that of a goldfish, the charts were virtually indistinguishable. The catfish had not altered its ECG for protection. And, when Welzel and Schuster checked how responsive the electric catfish's heart is when mildly stimulated, a 0.12 mA current was sufficient to trigger a regular heartbeat, identical to the goldfish heart's stimulation threshold. But the real test came when the pair checked how resilient the catfish heart was to more significant electric shocks – sufficient to trigger a life-threatening irregular heartbeat in other fish – and surprisingly, the electric catfish hearts were equally as vulnerable. A 3.03 mA shock was sufficient to send catfish and goldfish hearts racing erratically. Even though electric catfish are immune to the fatal power of their own bolts of electricity, their hearts appear to be as vulnerable as the hearts of any creature they intend to stun.So, how do the extraordinary river dwellers protect their hearts from their own lethal discharges? Schuster suggests that the heart and other vulnerable tissues, such as the brain and sensory organs, could be wrapped in insulation; however, he has yet to find any evidence of such a material. ‘Either the hypothetical insulators are highly efficient or the actual mechanism of how such layers protect the hearts of living electric catfish is more complex’, Welzel says. Meanwhile, electric catfish continue to be immune to their own deadly discharges regardless of vulnerability at the heart of the matter.