A novel mechanism controlling heart rate in the ancestral Pacific hagfish

Introducing a novel mechanism to control heart rate in the ancestral Pacific hagfish“. Christopher M. Wilson, Jinae N. Roa, Georgina K. Cox, Martin Tresguerres and Anthony P. Farrell. Journal of Experimental Biology (2016) 219, 3227-3236 doi:10.1242/jeb.138198


UBC researchers, Dr. Christopher Wilson,  Dr. Georgina Cox, and Dr. Anthony Farrell, and UC San Diego researchers Jinae Roa and Dr. Martin Tresguerres report evidence for a novel mechanism never previously implicated in chordate cardiac control – a bicarbonate-activated, soluble adenylyl cyclase (sAC)-dependent mechanism in Pacific Hagfish (Eptatretus stoutii).

Hagfishes origin dates back 0.5 billion years. Beyond their basal position in vertebrate evolution, hagfishes are biologically intriguing because of their anoxia tolerance and legendary ability to produce copious amounts of slime.
 

BMSC Research Coordinator, Eric Clelland, collecing hagfish (and slime!).

Hagfishes possess the most ancestral craniate-type heart, yet unlike all other known craniate hearts, the hagfish heart receives no direct neural stimulation. Despite this, their heart rate can vary four-fold during a prolonged, anoxic challenge followed by a normoxic recovery period, with heart rate decreasing in anoxia, and increasing beyond routine rates during recovery. It is surprising that the hagfish can regulate its heart rate over such a large range without any cardiac innervation.

The present study documents the discovery of a novel control pathway to increase heart rate, and is the first to report a chordate heart implicating HCO3 − stimulation of intracellular sAC to produce cAMP and stimulate the spontaneous heartbeat. This discovery should spur further research in the functional roles of sAC in vertebrate hearts to determine whether this control mechanism is more widespread in the lineage, or just another remarkable aspect of the biology of hagfishes.