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Acetylcholine (ACh) interacts with a muscarinic receptor of the subtypes indicated to induce various responses. The M₂ and M₄ muscarinic acetylcholine receptors (mAChRs) interact with the α subunit of GTP-binding protein, G_i. When ACh binds, Gα_i dissociates from βγ and inhibits adenylyl cyclase (AC). The M₁, M₃ and M₅ mAChRs interact with GTP-binding proteins in the G_q and G₁₁ family. The Gα_q and α₁₁ subunits activate phosphoinositide-specific phospholipase C (PI-PLC). The M₂ and M₄ mAChRs regulate inwardly rectifying K⁺ channels through the βγ subunit of G_i or G_o. Diffusible second messengers formed within the cell include cAMP, inositol trisphosphate (IP ₃ ) and diacylglycerol (DAG). IP₃ is generated from phosphatidylinositol bisphosphate (PIP₂). NE, norepinephrine; β-AdrR, β-adrenergic receptor; PI, phosphatidylinositol; PIP, phosphatidylinositol-4-phosphate; PIP ₂, phosphatidylinositol-4,5-bisphosphate.

Summary of the regulation of cortical microvessels from cells located in subcortical areas and within the cerebral cortex. The possibility that interneurons also induce the release of vasoactive molecules from astrocytes is not included for clarity purposes. The known or suggested vasoactive mediators and the vascular receptors on which neuronal or astroglial (PGE₂ and 20-HETE) signaling molecules are believed to act to induce dilatation or constriction are illustrated. Note that GABA has been shown to dilate, via GABAA receptors, pial vessels but not intracortical microvessels [12]. M5, muscarinic receptors that mediate dilatation of cerebral microvessels;VAPC1, dilatory receptor for VIP in brain vessels; NPY1, NPY receptor mediating cerebral vasoconstriction; SSR2/4, somatostatin receptors on smooth muscle cells of cortical microvessels that can mediate contraction [4]; 5-HT1B, contractile receptor for 5-HT, but note that a dilatory response mediated by the same receptor has also been reported [11]; EP4, dilatory receptors for PGE₂ in brain vessels [7]; ?, the cerebrovascular receptor for 20-HETE is still unknown. Used with permission from J Appl Physiol 2006;100:1059–1064.

Comparison of the inhibitory effect of genistein on ROCE and SOCE endogenous to HEK cells, COS-7 cells, and mouse embryonic fibroblasts lacking the indicated members of the src-family of tyrosine kinases. In the experiments shown in this and the other figures, ROCE was assessed in cells expressing the indicated Gq-coupled GPCR in transient or stable form, loading the cells that had been plated on coverslips with fura2 and subjecting these cells to a Ca²⁺ mobilization protocol in which the PLC system was activated by the cognate receptor agonist (carbachol [CCh] for the M5 muscarinic receptor and arginine vasopressin [AVP] for the V1a vasopressin receptor) in the absence of external Ca²⁺. [Ca²⁺]_i changes were then followed by video spectromicroscopy to record Ca²⁺ release from internal stores and allowing [Ca²⁺]_i to return to near basal levels. At this point, Ca²⁺ was added to the external medium and influx of Ca²⁺ leading to increase in [Ca²⁺]_i representing ROCE, was monitored for the indicated times. When drugs such as genistein or KB-R7943 (see below) were added, they were present through the first and second phases of the [Ca²⁺]_i changes. Note that only the Ca²⁺ entry phases are shown. In none of the experiments shown in this or the other figures did the presence of tyrosine kinase or Na-Ca exchange inhibitors affect significantly the IP₃- or thapsigargin-induced Ca²⁺ release from the endogenous stores. SOCE was assessed by substituting the GPCR agonist for thapsigargin. Gd³⁺ (5–10 μM) was added when TRPC-mediated ROCE was measured. At this concentration of Gd³⁺ TRPC3, 5, 6, and 7 mediated Ca²⁺ entry is unaffected, but endogenous ROCE is inhibited. Data on effects of genistein are either unpublished or adapted from Kawasaki et al. [80]