Resting cardiac sympathetic firing frequencies suppress terminal norepinephrine transporter uptake
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Resting cardiac sympathetic firing frequencies suppress terminal norepinephrine transporter uptake. / Cao, Lily L; Marshall, Janice M; Fabritz, Larissa; Brain, Keith L.
In: AUTON NEUROSCI-BASIC, Vol. 232, 102794, 05.2021.Research output: SCORING: Contribution to journal › SCORING: Journal article › Research › peer-review
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TY - JOUR
T1 - Resting cardiac sympathetic firing frequencies suppress terminal norepinephrine transporter uptake
AU - Cao, Lily L
AU - Marshall, Janice M
AU - Fabritz, Larissa
AU - Brain, Keith L
N1 - Copyright © 2021 Elsevier B.V. All rights reserved.
PY - 2021/5
Y1 - 2021/5
N2 - The prejunctional norepinephrine transporter (NET) is responsible for the clearance of released norepinephrine (NE) back into the sympathetic nerve terminal. NET regulation must be tightly controlled as variations could have important implications for neurotransmission. Thus far, the effects of sympathetic neuronal activity on NET function have been unclear. Here, we optically monitor single-terminal cardiac NET activity ex vivo in response to a broad range of sympathetic postganglionic action potential (AP) firing frequencies. Isolated murine left atrial appendages were loaded with a fluorescent NET substrate [Neurotransmitter Transporter Uptake Assay (NTUA)] and imaged with confocal microscopy. Sympathetic APs were induced with electrical field stimulation at 0.2-10 Hz (0.1-0.2 ms pulse width). Exogenous NE was applied during the NTUA uptake- and washout phases to investigate substrate competition and displacement, respectively, on transport. Single-terminal NET reuptake rate was rapidly suppressed in a frequency-dependent manner with an inhibitory EF50 of 0.9 Hz. At 2 Hz, the effect was reversed by the α2-adrenoceptor antagonist yohimbine (1 μM) (p < 0.01) with no further effect imposed by the muscarinic receptor antagonist atropine (1 μM). Additionally, high exogenous NE concentrations abolished NET reuptake (1 μM NE; p < 0.0001) and displaced terminal specific NTUA during washout (1-100 μM NE; p < 0.0001). We have also identified α2-adrenoceptor-induced suppression of NET reuptake rate during resting stimulation frequencies, which could oppose the effect of autoinhibition-mediated suppression of exocytosis and thus amplify the effects of sympathetic drive on cardiac function.
AB - The prejunctional norepinephrine transporter (NET) is responsible for the clearance of released norepinephrine (NE) back into the sympathetic nerve terminal. NET regulation must be tightly controlled as variations could have important implications for neurotransmission. Thus far, the effects of sympathetic neuronal activity on NET function have been unclear. Here, we optically monitor single-terminal cardiac NET activity ex vivo in response to a broad range of sympathetic postganglionic action potential (AP) firing frequencies. Isolated murine left atrial appendages were loaded with a fluorescent NET substrate [Neurotransmitter Transporter Uptake Assay (NTUA)] and imaged with confocal microscopy. Sympathetic APs were induced with electrical field stimulation at 0.2-10 Hz (0.1-0.2 ms pulse width). Exogenous NE was applied during the NTUA uptake- and washout phases to investigate substrate competition and displacement, respectively, on transport. Single-terminal NET reuptake rate was rapidly suppressed in a frequency-dependent manner with an inhibitory EF50 of 0.9 Hz. At 2 Hz, the effect was reversed by the α2-adrenoceptor antagonist yohimbine (1 μM) (p < 0.01) with no further effect imposed by the muscarinic receptor antagonist atropine (1 μM). Additionally, high exogenous NE concentrations abolished NET reuptake (1 μM NE; p < 0.0001) and displaced terminal specific NTUA during washout (1-100 μM NE; p < 0.0001). We have also identified α2-adrenoceptor-induced suppression of NET reuptake rate during resting stimulation frequencies, which could oppose the effect of autoinhibition-mediated suppression of exocytosis and thus amplify the effects of sympathetic drive on cardiac function.
KW - Animals
KW - Biological Transport
KW - Heart
KW - Mice
KW - Norepinephrine
KW - Norepinephrine Plasma Membrane Transport Proteins
KW - Sympathetic Nervous System
U2 - 10.1016/j.autneu.2021.102794
DO - 10.1016/j.autneu.2021.102794
M3 - SCORING: Journal article
C2 - 33714751
VL - 232
JO - AUTON NEUROSCI-BASIC
JF - AUTON NEUROSCI-BASIC
SN - 1566-0702
M1 - 102794
ER -