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Potentiation of large conductance, Ca2+-activated K+ (BK) channels by α5β1 integrin activation in arteriolar smooth muscle

By Xin Wu, Yan Yang, Peichun Gui, Yoshiro Sohma, Gerald A Meininger, George E Davis, Andrew P Braun and Michael J Davis

Abstract

Injury/degradation of the extracellular matrix (ECM) is associated with vascular wall remodelling and impaired reactivity, a process in which altered ECM–integrin interactions play key roles. Previously, we found that peptides containing the RGD integrin-binding sequence produce sustained vasodilatation of rat skeletal muscle arterioles. Here, we tested the hypothesis that RGD ligands work through α5β1 integrin to modulate the activity of large conductance, Ca2+-activated K+ (BK) channels in arteriolar smooth muscle. K+ currents were recorded in single arteriolar myocytes using whole-cell and single-channel patch clamp methods. Activation of α5β1 integrin by an appropriate, insoluble α5β1 antibody resulted in a 30–50% increase in the amplitude of iberiotoxin (IBTX)-sensitive, whole-cell K+ current. Current potentiation occurred 1–8 min after bead–antibody application to the cell surface. Similarly, the endogenous α5β1 integrin ligand fibronectin (FN) potentiated IBTX-sensitive K+ current by 26%. Current potentiation was blocked by the c-Src inhibitor PP2 but not by PP3 (0.1–1 μm). In cell-attached patches, number of open channels × open probability (NPo) of a 230–250 pS K+ channel was significantly increased after FN application locally to the external surface of cell-attached patches through the recording pipette. In excised, inside-out patches, the same method of FN application led to large, significant increases in NPo and caused a leftward shift in the NPo–voltage relationship at constant [Ca2+]. PP2 (but not PP3) nearly abolished the effect of FN on channel activity, suggesting that signalling between the integrin and channel involved an increase in Ca2+sensitivity of the channel via a membrane-delimited pathway. The effects of α5β1 integrin activation on both whole-cell and single-channel BK currents could be reproduced in HEK 293 cells expressing the BK channel α-subunit. This is the first demonstration at the single-channel level that integrin signalling can regulate an ion channel. Our results show that α5β1 integrin activation potentiates BK channel activity in vascular smooth muscle through both Ca2+- and c-Src-dependent mechanisms. This mechanism is likely to play a role in the arteriolar dilatation and impaired vascular reactivity associated with ECM degradation

Topics: Cardiovascular
Publisher: Blackwell Science Inc
OAI identifier: oai:pubmedcentral.nih.gov:2375690
Provided by: PubMed Central
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