N-type and P/Q-type calcium channels regulate differentially the release of noradrenaline, ATP and beta-NAD in blood vessels.

Using HPLC techniques we evaluated the electrical field stimulation-evoked overflow of noradrenaline (NA), adenosine 5'-triphosphate (ATP), and beta-nicotinamide adenine dinucleotide (beta-NAD) in the presence of low nanomolar concentrations of omega-conotoxin GVIA or omega-agatoxin IVA in the canine mesenteric arteries and veins. omega-conotoxin GVIA abolished the evoked overflow of NA and beta-NAD in artery and vein, whereas the evoked overflow of ATP remained unchanged in the presence of omega-conotoxin GVIA. omega-agatoxin IVA significantly reduced the evoked overflow of ATP and beta-NAD. The overflow of NA remained largely unaffected by omega-agatoxin IVA, except at 16Hz in the vein where the overflow of NA was reduced by about 50%. Artery and vein exhibited similar expression levels of the alpha(1B) (CaV2.2, N-type) subunit, whereas the vein showed greater levels of the alpha(1A) (CaV2.1, P/Q-type) subunit than artery. Therefore, there are at least two release sites for NA, beta-NAD and ATP in the canine mesenteric artery and vein: an N-type-associated site releasing primarily NA, beta-NAD and some ATP, and a P/Q-type-associated site releasing ATP, beta-NAD and some NA. The N-type-mediated mechanisms are equally expressed in artery and vein, whereas the P/Q-type-mediated mechanisms are more pronounced in the vein and may ensure additional neurotransmitter release at higher levels of neural activity. In artery, beta-NAD caused a dual effect consisting of vasodilatation or vasoconstriction depending on concentrations, whereas vein responded with vasodilatation only. In contrast, ATP caused vasoconstriction in both vessels. beta-NAD and ATP may mediate disparate functions in the canine mesenteric resistive and capacitative circulations.