Glutamate regulates Ca2+ signals in smooth muscle cells of newborn piglet brain slice arterioles through astrocyte- and heme oxygenase-dependent mechanisms

Abstract

Glutamate is the principal cerebral excitatory neurotransmitter and dilates cerebral arterioles to match blood flow to neural activity. Arterial contractility is regulated by local and global Ca2+ signals that occur in smooth muscle cells, but modulation of these signals by glutamate is poorly understood. Here, using high-speed confocal imaging, we measured the Ca2+ signals that occur in arteriole smooth muscle cells of newborn piglet tangential brain slices, studied signal regulation by glutamate, and investigated the physiological function of heme oxygenase (HO) and carbon monoxide (CO) in these responses. Glutamate elevated Ca2+ spark frequency by ∼188% and reduced global intracellular Ca2+ concentration ([Ca2+]i) to ∼76% of control but did not alter Ca2+ wave frequency in brain arteriole smooth muscle cells. Isolation of cerebral arterioles from brain slices abolished glutamate-induced Ca2+ signal modulation. In slices treated with l-2-α-aminoadipic acid, a glial toxin, glutamate did not alter Ca2+ sparks or global [Ca2+]i but did activate Ca2+ waves. This shift in Ca2+ signal modulation by glutamate did not occur in slices treated with d-2-α-aminoadipic acid, an inactive isomer of l-2-α-aminoadipic acid. In the presence of chromium mesoporphyrin, a HO blocker, glutamate inhibited Ca2+ sparks and Ca2+ waves and did not alter global [Ca2+]i. In isolated arterioles, CORM-3 [tricarbonylchloro(glycinato)ruthenium(II)], a CO donor, activated Ca2+ sparks and reduced global [Ca2+]i. These effects were blocked by 1 H-(1,2,4)-oxadiazolo-(4,3-a)-quinoxalin-1-one, a soluble guanylyl cyclase inhibitor. Collectively, these data indicate that glutamate can modulate Ca2+ sparks, Ca2+ waves, and global [Ca2+]i in arteriole smooth muscle cells via mechanisms that require astrocytes and HO. These data also indicate that soluble guanylyl cyclase is involved in CO activation of Ca2+ sparks in arteriole smooth muscle cells.