Effects of the polyamine spermine on arterial chemoreception.
Polyamines modulate many biological functions. Here we report a novel inhibitory modulation by spermine of catecholamine release by the rat carotid body and have identified the molecular mechanism underpinning it. We used molecular (RT-PCR and confocal microscopy) and functional (i.e., neurotransmitter release, patch clamp recording and calcium imaging) approaches to test the involvement of: (i) voltage-dependent calcium channels, and; (ii) the extracellular calcium-sensing receptor, CaR, a G protein-coupled receptor which is also activated by polyamines. RT-PCR and immunohistochemistry of isolated carotid bodies revealed that only Ca(v)1.2 and Ca(v)2.2 were expressed in type 1 cells while Ca(v)1.3, Ca(v)1.4, Ca(v)2.1, Ca(v)2.3 and Ca(v)3.1, Ca(v)3.2 and Ca(v)3.3, could not be detected. CaR expression was detected exclusively in the nerve endings. In isolated carotid bodies, the hypoxia-dependent (7% O(2) for 10 minutes) and depolarization-evoked catecholamine release were partially suppressed by pre- (and co)-incubation with 500microM spermine. In dissociated type 1 glomus cells intracellular calcium concentration did not change following spermine treatment, but this polyamine did inhibit the depolarisation-evoked calcium influx. Whole-cell patch clamp recordings of HEK293 cells stably transfected with Ca(v)1.2 demonstrated that spermine inhibits this calcium channel. Interestingly, this inhibition was not apparent if the extracellular solution contained a concentration of Ba(2) above 2 mM as the charge carrier. In conclusion, spermine attenuates catecholamine release by the carotid body principally via inhibition of Ca(v)1.2. This mechanism may represent a negative feedback, which limits transmitter release during hypoxia.
Cayzac
S
S
Cardiff University, Museum Avenue, Cardiff CF10 3US, UK. cayzacs@cardiff.ac.uk
Rocher
A
A
Obeso
A
A
Gonzalez
C
C
Kemp
P J
PJ
Riccardi
D
D
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism; D002339:Carotid Arteries / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D002344:Carotid Body / Q000187:drug effects* / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism; D002460:Cell Line; D004553:Electric Conductivity; D005786:Gene Expression Regulation / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D044169:Receptors, Calcium-Sensing / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013096:Spermine / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002395:Catecholamines; D044169:Receptors, Calcium-Sensing; D011994:Recombinant Proteins; D013096:Spermine; D002118:Calcium