Potentiation of large conductance, Ca 2+ ‐activated K + (BK) channels by α5β1 integrin activation in arteriolar smooth muscle

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, Ca 2+ ‐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 μ m ). In cell‐attached patches, number of open channels × open probability ( NP o ) 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 NP o and caused a leftward shift in the NP o –voltage relationship at constant [Ca 2+ ]. 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 Ca 2+ 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 Ca 2+ ‐ 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.