Purinergic signaling triggers endfoot high-amplitude Ca²⁺ signals and causes inversion of neurovascular coupling after subarachnoid hemorrhage

Abstract

Neurovascular coupling supports brain metabolism by matching focal increases in neuronal activity with local arteriolar dilation. Previously, we demonstrated that an emergence of spontaneous endfoot high-amplitude Ca 2þ signals (eHACSs) caused a pathologic shift in neurovascular coupling from vasodilation to vasoconstriction in brain slices obtained from subarachnoid hemorrhage model animals. Extracellular purine nucleotides (e.g., ATP) can trigger astrocyte Ca 2þ oscillations and may be elevated following subarachnoid hemorrhage. Here, the role of purinergic signaling in subarachnoid hemorrhage-induced eHACSs and inversion of neurovascular coupling was examined by imaging parenchymal arteriolar diameter and astrocyte Ca 2þ signals in rat brain slices using two-photon fluorescent and infrared-differential interference contrast microscopy. We report that broad-spectrum inhibition of purinergic (P2) receptors using suramin blocked eHACSs and restored vasodilatory neurovascular coupling after subarachnoid hemorrhage. Importantly, eHACSs were also abolished using a cocktail of inhibitors targeting G q -coupled P2Y receptors. Further, activation of P2Y receptors in brain slices from un-operated animals triggered high-amplitude Ca 2þ events resembling eHACSs and disrupted neurovascular coupling. Neither tetrodotoxin nor bafilomycin A1 affected eHACSs suggesting that purine nucleotides are not released by ongoing neurotransmission and/or vesicular release after subarachnoid hemorrhage. These results indicate that purinergic signaling via P2Y receptors contributes to subarachnoid hemorrhage-induced eHACSs and inversion of neurovascular coupling.

The yin and yang of KV channels in cerebral small vessel pathologies

“…This is consistent with our results showing that PAs isolated from the brains of SAH animals and pressurized ex vivo dilate in response to modest increases in extracellular K + . However, SAH is associated with an inversion of NVC in animal models; that is, instead of causing vasodilation, neuronal activation causes vasoconstriction in these animals, both in brain slices and in vivo . We have proposed that this inversion of NVC is the result of a pathological increase in basal [K + ] o reflecting enhanced K + efflux by astrocytic endfeet, rather than impaired K IR function.…”

“…When summed with neurally evoked K + efflux, the net elevation in basal [K + ] o leads to a more depolarized SMC E K that lies outside of the influence of the K IR window. Thus, the polarity of the vascular response is switched from dilation to constriction due to V m depolarization and enhanced Ca 2+ entry through VDCCs …”

Inversion of neurovascular coupling after subarachnoid hemorrhage in vivo

“…Broad-spectrum inhibition of purinergic (P2) receptors and targeted inhibition of G q -coupled P2Y receptors have been shown to abolish highamplitude Ca 2þ signals after SAH, but the purine nucleotides responsible were shown not to be released by neurotransmission after SAH. 32 This suggests that the therapeutic targeting of purinergic signaling in astrocytes could be complementary to an early rescue of NO reactivity.…”

mRNA Expression Profiles from Whole Blood Associated with Vasospasm in Patients with Subarachnoid Hemorrhage

“…The distance between spheres in the 3-D space shows their differences based on the expression pattern. Each of the two ellipsoids represents a two-standard deviation space from the mean of each group of samples inhibition using suramin restored vasodilatory neurovascular coupling after SAH [13].…”

“…P2Y purinergic receptor signaling was also associated with vasospasm. In vitro studies suggest purinergic signaling triggers astrocyte end foot high-amplitude calcium signaling and causes inversion of neurovascular coupling after SAH [ 13 ]. P2 receptor inhibition using suramin restored vasodilatory neurovascular coupling after SAH [ 13 ].…”