CaV2.3 Mediate ATP Release from Rat Tail Artery Sympathetic Nerves

Abstract

Peripheral sympathetic nerves are essential for regulating homeostatic control of target organs, such as the tone of blood vessels, and many details of the molecular organization of peripheral sympathetic nerve varicosities remain to be defined. Unlike central synapses, peripheral varicosities typically exhibit co-transmission of multiple neurotransmitters. Several lines of evidence show co-transmission of the sympathetic transmitters norepinephrine (NE) or ATP is mediated by the preferential association of separate pools of vesicles with CaV2.1 and CaV2.2 isoforms that provide the Ca2+ entry for vesicle release. CaV2.3 is a closely related channel that has been studied in several central synapses, but its role in peripheral sympathetic nerves is largely unknown. Using confocal microscopy to study perivascular nerves, we previously found that ATP and NE are stored in segregated pools of vesicles. Further, we found that CaV2.3 are expressed in rat tail perivascular sympathetic nerves and that they co-localize with vesicles expressing the vesicular nucleotide transporter (VNUT) that loads ATP into vesicles rather than vesicle harbouring the NE-transporting vesicular monoamine translocase 2 (VMAT2). We now report one of the first functional characterizations of CaV2.3 in perivascular nerves. We assessed the functional role of CaV2.3 in field-stimulated isometric force generated by rat tail arteries in response to pulse-number ramps (3-100 pulses, 20 Hz). Inhibition of vasoconstriction with the CaV2.3 blocker SNX-482 (250 nM) mimicked the effect of blocking smooth muscle P2X receptors with suramin while blocking α-adrenergic receptors with phentolamine productive a distinct inhibitory profile. These functional tests were corroborated by immuno-fluorescence microscopy showing that CaV2.3 immunoreactivity correlated with the sensitivity of individual blood vessels to suramin and SNX-482.