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The group led by Ming Lei has discovered that the heart can regulate its own rhythm by releasing adrenaline (epinephrine) from a specialised kind of heart muscle cell that contains the enzyme that makes adrenaline.

Images: (left) The localisation of the Pmnt+ cells in the mouse heart. (right) Optogenetic stimulation (blue line) of the Pnmt+ cells showing increased rate of contractions in the left ventricle (LV), but not in the right ventricle (RV)

Adrenergic cells are a collection of neuroendocrine cells that occur in endocrine tissues (such as the adrenal medulla) and brain. A hallmark of these cells is that they contain phenylethanolamine N-methyltransferase (PNMT), the enzyme that converts noradrenaline to adrenaline (epinephrine). The adrenergic cells are critical for the physiological response to stress (ie fight-or-flight) by releasing adrenaline into the blood, which increases the strength and rate of beating of the heart. Surprisingly, such endocrine function may also be present in the heart itself. Dr Ming Lei’s group recently found that a subpopulation of mouse heart muscle cells (cardiomyocytes) contain PNMT. These Pnmt+ cardiomyocytes are highly abundant in the left side of the heart and the conduction system, suggesting that localized cardiac adrenergic signalling may be carried out by these cells in special regions of the heart. It was shown that optogenetic stimulation of these Pnmt+ cells led to an increased rate of beating of the left ventricle, but not the right ventricle, consistent with the release of adrenaline from these specialized cells. It remains to be discovered how these cells are activated to release adrenaline in the living animal and what their physiological role might be.

Optogenetic control of heart rhythm by selective stimulation of cardiomyocytes derived from Pnmt(+) cells in murine heart. Y Wang, WK Lin, W Crawford, H Ni, EL Bolton, H Khan, J Shanks, G Bub, X Wang, DJ Paterson, H Zhang, A Galione, SN Ebert, DA Terrar and M Lei. Sci Rep (2017) 7: 40687.

May 2018