Injury/degradation of the extracellular matrix (ECM) is associated with vascular wall remodeling 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 vasodilation of rat skeletal muscle arterioles. Here, we tested the hypothesis that RGD ligands work through 51 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 51 integrin by an appropriate, insoluble 51 antibody resulted in 30-50% increase in the amplitude of IBTX-sensitive, whole-cell K+ current. Current potentiation occurred 1-8 min after bead/antibody application to the cell surface. Similarly, the endogenous 51 integrin ligand, fibronectin (FN), potentiated IBTX-sensitive K+ current by up 26%. Current potentiation was blocked by the c-Src inhibitor, PP2, but not by PP3 (0.1-1 µM). In cell-attached patches, the N•Po 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 a large, significant increase in N•Po and caused a leftward shift in the N•Po-voltage relationship at constant [Ca2+]. PP2 (but not PP3) nearly abolished the effect of FN on channel activity, suggesting that signaling between the integrin and channel involved an increase in Ca2+-sensitivity of the channel via a membrane-delimited pathway. The effects of 51 integrin activation on both whole-cell and single-channel BK currents could be reproduced in HEK 293 cells expressing the BK channel -subunit. This is the first demonstration at the single channel level that integrin signaling can regulate an ion channel. Our results show that 51 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 dilation and impaired vascular reactivity associated with ECM degradation.