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

Abstract

Using HPLC techniques we evaluated the electrical field stimulation-evoked overflow of noradrenaline (NA), adenosine 5′-triphosphate (ATP), and β-nicotinamide adenine dinucleotide (β-NAD) in the presence of low nanomolar concentrations of ω-conotoxin GVIA or ω-agatoxin IVA in the canine mesenteric arteries and veins. ω-conotoxin GVIA abolished the evoked overflow of NA and β-NAD in artery and vein, whereas the evoked overflow of ATP remained unchanged in the presence of ω-conotoxin GVIA. ω-agatoxin IVA significantly reduced the evoked overflow of ATP and β-NAD. The overflow of NA remained largely unaffected by ω-agatoxin IVA, except at 16 Hz in the vein where the overflow of NA was reduced by about 50%. Artery and vein exhibited similar expression levels of the α 1B (CaV2.2, N-type) subunit, whereas the vein showed greater levels of the α 1A (CaV2.1, P/Q-type) subunit than artery. Therefore, there are at least two release sites for NA, β-NAD and ATP in the canine mesenteric artery and vein: an N-type-associated site releasing primarily NA, β-NAD and some ATP, and a P/Q-type-associated site releasing ATP, β-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, β-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. β-NAD and ATP may mediate disparate functions in the canine mesenteric resistive and capacitative circulations.

Purinergic Signaling and Blood Vessels in Health and Disease

“…N-type and P/Q-type calcium channels regulate differentially the release of NA, ATP, and b-NAD from sympathetic nerves supplying canine mesenteric blood vessels; N-type channels are equally expressed by arteries and veins, whereas P/Q-type channels are more pronounced in veins (Smyth et al, 2009).…”

The purinergic neurotransmitter revisited: A single substance or multiple players?

“…For example, in the canine mesentery, α 2 -adrenoceptor agonists significantly reduced the release of NE but had no effect on ATP release at low frequencies of EFS, suggesting release from different sites (Bobalova & Mutafova-Yambolieva, 2001b). In addition, Smyth et al, 2009 showed in canine mesenteric blood vessels that release of NE was primarily regulated by N-type Ca 2+ channels whereas release of ATP was regulated mainly by P/Q-type Ca 2+ channels. Therefore NE and ATP may not be stored in and released from the same population of synaptic vesicles in mesenteric vasculature.…”

“…The study concluded that in this blood vessel ATP originates from a number of sources including nerve terminals, endothelium, and smooth muscle. Finally, as discussed above, highly-sensitive HPLC methodologies for purine detection proved to be instrumental in characterizing purinergic neurotransmission and cotransmission in a number of blood vessels, including the guinea-pig mesenteric artery and vein (Bobalova & Mutafova-Yambolieva, 2001a), rat tail artery (Westfall et al, 1987; Mutafova-Yambolieva & Westfall, 1998), rabbit aorta (Sedaa et al, 1990), rabbit pulmonary artery (Mohri et al, 1993), and canine mesenteric arteries and veins (Bobalova & Mutafova-Yambolieva, 2001b; Bobalova et al, 2002; Smyth et al, 2004; Smyth et al, 2009). The EFS-evoked release of ATP was reduced by TTX or guanethidine in the rabbit aorta (Sedaa et al, 1990), rat tail artery (Mutafova-Yambolieva & Westfall, 1998), and guinea-pig and canine mesenteric arteries and veins (Bobalova & Mutafova-Yambolieva, 2001a; Bobalova & Mutafova-Yambolieva, 2001b).…”

“…Therefore NE and ATP may not be stored in and released from the same population of synaptic vesicles in mesenteric vasculature. It should be pointed out that in the canine mesenteric blood vessels EFS evoked release of NAD + along with ATP and NE, in a frequency-dependent and neurotoxin-sensitive manner (Smyth et al, 2004; Smyth et al, 2009). Interestingly, the release of NAD + , like NE, was reduced by the N-type Ca 2+ channel inhibitor ω-conotoxin GVIA, whereas the release of ATP was not affected by ω-conotoxin GVIA in either artery or vein (Smyth et al, 2009).…”

Neuronal and extraneuronal release of ATP and NAD+ in smooth muscle

“…On the other hand, in colonic muscles from mouse, monkey and human, only the evoked overflow of NAD + , but not of ATP, demonstrated characteristics of neuronal release (22,23). In blood vessels inhibition of neuronal N-type voltage-dependent Ca 2+ channels blocked the release of NAD + (and norepinephrine), but not of ATP (50). Therefore, purine neurotransmission in smooth muscle is more complex than previously thought.…”