Vasoactive effects of soluble matrix proteins and integrin-binding peptides on arterioles are mediated by αvβ3 and α5β1 integrins. To examine the underlying mechanisms, we measured L-type Ca2+ channel current in arteriolar smooth muscle cells in response to integrin ligands. Whole-cell, inward Ba2+ currents were inhibited after application of soluble cyclic RGD peptide, vitronectin (VN), fibronectin (FN), either of two anti–β3 integrin antibodies, or monovalent β3 antibody. With VN or β3 antibody coated onto microbeads and presented as an insoluble ligand, current was also inhibited. In contrast, beads coated with FN or α5 antibody produced significant enhancement of current after bead attachment. Soluble α5 antibody had no effect on current but blocked the increase in current evoked by FN-coated beads and enhanced current when applied in combination with an appropriate IgG. The data suggest that αvβ3 and α5β1 integrins are differentially linked through intracellular signaling pathways to the L-type Ca2+ channel and thereby alter control of Ca2+ influx in vascular smooth muscle. This would account for the vasoactive effects of integrin ligands on arterioles and provide a potential mechanism for wound recognition during tissue injury.

The L-type calcium channel is the major calcium influx pathway in vascular smooth muscle and is regulated by integrin ligands, suggesting an important link between extracellular matrix and vascular tone regulation in tissue injury and remodeling. We examined the role of integrin-linked tyrosine kinases and focal adhesion proteins in regulation of L-type calcium current in single vascular myocytes. Soluble tyrosine kinase inhibitors blocked the increase in current produced by ␣ 5 integrin antibody or fibronectin, whereas tyrosine phosphatase inhibition enhanced the effect. Cell dialysis with an antibody to focal adhesion kinase or with FRNK, the C-terminal noncatalytic domain of focal adhesion kinase, produced moderate (24 or 18%, respectively) inhibition of basal current but much greater inhibition (63 or 68%, respectively) of integrin-enhanced current. A c-Src antibody and peptide inhibitors of the Src homology-2 domain or a putative Src tyrosine phosphorylation site on the channel produced similar inhibition. Antibodies to the cytoskeletal proteins paxillin and vinculin, but not ␣-actinin, inhibited integrin-dependent current by 65-80%. Therefore, ␣ 5 ␤ 1 integrin appears to regulate a tyrosine phosphorylation cascade involving Src and various focal adhesion proteins that control the function of the L-type calcium channel. This interaction may represent a novel mechanism for control of calcium influx in vascular smooth muscle and other cell types.Mechanical forces are known to stimulate a number of cell signaling pathways, including those initiated by or resulting in ion channel activation. Several types of ion channels exhibit mechanosensitivity, but the mechanisms underlying their gating remain unclear. Membrane tension changes induced by physiologically relevant forces may not be sufficiently large to gate channels directly in eukaryotic cells (1). Thus, it is likely that mechanically advantageous associations with cytoskeletal or other membrane-bound proteins play a key role in control of gating. However, some mechanism must exist to integrate mechanosensitive gating behavior with the primary regulatory mechanism for channel gating, which is phosphorylation of channel proteins by intracellular kinases (2).Integrins are potential force transduction proteins because they span the plasma membrane and link the extracellular matrix (ECM) 1 to the underlying actin cytoskeleton (CSK) in specialized focal contact regions. Stress applied through integrin-specific adhesion sites increases cytoskeletal stiffening (3), activates second messenger formation (4) and initiates ribosomal and mRNA recruitment to focal adhesions (5). Integrin clustering by multivalent ligands, including ECM proteins, induces recruitment of CSK proteins including vinculin, talin, paxillin and tensin to the focal contact (6, 7). Kinases such as focal adhesion kinase (FAK), Src, PLC-␥, and Rho GTPase, as well as adaptor proteins such as Grb2, Sos, and Shc, are also recruited to the ECM-integrin binding site (8, 9). Subsequently, phosphorylation...

The ovarian cycle affects susceptibility to behavioral and neurologic conditions. The molecular mechanisms underlying these changes are poorly understood. Deficits in cyclical fluctuations in steroid hormones and receptor plasticity play a central role in physiologic and pathophysiologic menstrual conditions. It has been suggested that synaptic GABA A receptors mediate phasic inhibition in the hippocampus and extrasynaptic receptors mediate tonic inhibition in the dentate gyrus. Here we report a novel role of extrasynaptic d-containing GABA A receptors as crucial mediators of the estrous cycle-related changes in neuronal excitability in mice, with hippocampus subfield specificity. In molecular and immunofluorescence studies, a significant increase occurred in d-subunit, but not a4-and g2-subunits, in the dentate gyrus during diestrus. However, d-subunit upregulation was not evident in the CA1 region. The d-subunit expression was undiminished by age and ovariectomy and in mice lacking progesterone receptors, but it was significantly reduced by finasteride, a neurosteroid synthesis inhibitor. Electrophysiologic studies confirmed greater potentiation of GABA currents by progesterone-derived neurosteroid allopregnanolone in dissociated dentate gyrus granule cells in diestrus than in CA1 pyramidal cells. The baseline conductance and allopregnanolone potentiation of tonic currents in dentate granule cells from hippocampal slices were higher than in CA1 pyramidal cells. In behavioral studies, susceptibility to hippocampus kindling epileptogenesis was lower in mice during diestrus. These results demonstrate the estrous cycle-related plasticity of neurosteroidsensitive, d-containing GABA A receptors that mediate tonic inhibition and seizure susceptibility. These findings may provide novel insight on molecular cascades of menstrual disorders like catamenial epilepsy, premenstrual syndrome, and migraine.

Cells within the vascular wall connect their cytoskeleton to the extracellular matrix (ECM) through a family of cell surface receptors known as integrins. The ability of integrins to act as a link between the extracellular and intracellular environments allows transmission of inside-out and outside-in signals capable of modulating diverse vascular phenomena. In this review we summarize what is currently known about the involvement of integrins in the control of vascular tone, permeability and remodeling. We discuss the capacity of integrins to act as detectors of injury-generated molecules derived from ECM proteins, as well as the putative role of integrins as mechanosensors for shear and tension. Particular attention is given to the mechanisms responsible for linking integrins to the control of vascular tone, and we review the intracellular signaling pathways involved in effecting the vascular responses elicited by integrin activation. Finally, the involvement of integrins in vascular remodeling and vascular disease is analyzed. Considerable evidence strongly indicates that integrins are involved in both acute and chronic vascular control. Understanding the elements and the sequence of events linking integrins with vasoregulation is important for deciphering phenomena such as the pressure-dependent myogenic response, flow-dependent changes in vascular diameter, and vascular remodeling as they occur in physiological and pathological conditions. Further understanding of the role of integrins in vascular control holds promise as new avenues for prophylactic and therapeutic manipulation of vascular phenomena.