Dual Spikes of Catecholamine Releases from Sympathetic Nerves in Rodent Heart Slices Following Hypoxia-Reperfusion as Recorded by a Novel Electrochemical Method

Sympathetic nerve in heart is essential in cardiac physiology and diseases, because it releases catecholamines to regulate cardiac cells including ventricular myocytes, atrial myocytes and vas through GPCRs. With a modified glass-insulated micro carbon fiber electrode (pegCFE), we record stimulus (depolarization or hypoxia)-signals via either amperometric current (Iamp) or fast cyclic voltammetry from the nerve terminals in rodent hearts, by a method termed cardiac Slice of ElectroChemistry (cSEC). We found that, (1) cSEC signal Iamp is dependent on CFE-voltage and extracellular Ca2+; (2) pharmacologically, Iamp is increased 40% by Yohimbine, and decreased 60% by reserpine; (3) electronic microscope detected dese core vesicles, tyrosine hydroxylase (TH) immunostaining and TH-GFP transgenic mice showed massive TH-signal in whole heart; (4) as determined by in-situ FCV, as well as microdialysis-based HPLC, NE and/or DHPG (a NE metabolic substance) were responsible for cSEC signals. These evidences establish that the evoked cSEC signals represent catecholamine releases from sympathetic nerves in heart slices. Using cSEC we discovered that hypoxia-reperfusion triggered dual spikes of catecholamine release at pH 7.4: first peak at 10s following hypoxia perfusion, second peak at 10s following normoxia perfusion. Finally, catecholamine release were reduced by 75% in ventricle slices from syt7(Ca2+ sensor)-KO versus WT mice, indicating cSEC may serve phenotyping of any sympathetic defects in cardiac disease animal models. Supported by NSFC, MOST 973 and PKU-THU-CLS