Cholinesterase inhibitors modify the activity of intrinsic cardiac neurons.
Cholinesterase inhibitors used to treat the symptoms of Alzheimer's disease (AD) inhibit both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), albeit to different degrees. Because central and peripheral neurons, including intrinsic cardiac neurons located on the surface of the mammalian heart, express both BuChE and AChE, we studied spontaneously active intrinsic cardiac neurons in the pig as a model to assess the effects of inhibition of AChE compared to BuChE. Neuroanatomical experiments showed that some porcine intrinsic cardiac neurons expressed AChE and/or BuChE. Enzyme kinetic experiments with cholinesterase inhibitors, namely, donepezil, galantamine, (+/-) huperzine A, metrifonate, rivastigmine, and tetrahydroaminoacridine, demonstrated that these compounds differentially inhibited porcine AChE and BuChE. Donepezil and (+/-) huperzine A were better reversible inhibitors of AChE, and galantamine equally inhibited both the enzymes. Tetrahydroaminoacridine was a better reversible inhibitor of BuChE. Rivastigmine caused more rapid inactivation of BuChE as compared to AChE. Neurophysiological studies showed that acetylcholine and butyrylcholine increase or decrease the spontaneous activity of the intrinsic cardiac neurons. Donepezil, galantamine, (+/-) huperzine A, and tetrahydroaminoacridine changed spontaneous neuronal activity by about 30-35 impulses per minute, while rivastigmine changed it by approximately 100 impulses per minute. It is concluded that (i) inhibition of AChE and BuChE directly affects the porcine intrinsic cardiac nervous system, (ii) the intrinsic cardiac nervous system represents a suitable model for examining the effects of cholinesterase inhibitors on mammalian neurons in vivo, and (iii) the activity of intrinsic cardiac neurons may be affected by pharmacological agents that inhibit cholinesterases.
Darvesh
Sultan
S
Department of Medicine (Neurology), Dalhousie University, Halifax, Nova Scotia, Canada. sultan.darvesh@dal.ca
Arora
Rakesh C
RC
Martin
Earl
E
Magee
David
D
Hopkins
David A
DA
Armour
J Andrew
JA
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002091:Butyrylcholinesterase / Q000187:drug effects / Q000378:metabolism*; D002794:Choline / Q000031:analogs & derivatives* / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000494:pharmacology*; D002802:Cholinesterases / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006321:Heart / Q000294:innervation* / Q000502:physiology; D007700:Kinetics; D008297:Male; D023421:Models, Animal; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D013379:Substrate Specificity; D013552:Swine; D009435:Synaptic Transmission / Q000187:drug effects
D002800:Cholinesterase Inhibitors; C017100:butyrylcholine; D002091:Butyrylcholinesterase; D002802:Cholinesterases; D002794:Choline; D000109:Acetylcholine