Potentiation of large conductance, Ca2+-activated K+ (BK) channels by alpha5beta1 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 alpha5beta1 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 alpha5beta1 integrin by an appropriate, insoluble alpha5beta1 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 alpha5beta1 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 mum). In cell-attached patches, number of open channels x 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 alpha5beta1 integrin activation on both whole-cell and single-channel BK currents could be reproduced in HEK 293 cells expressing the BK channel alpha-subunit. This is the first demonstration at the single-channel level that integrin signalling can regulate an ion channel. Our results show that alpha5beta1 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.
Wu
Xin
X
Department of Medical Pharmacology & Physiology, University of Missouri School of Medicine, 1 Hospital Dr, Rm M451, Columbia, MO 65212, USA. davismj@health.missouri.edu
Yang
Yan
Y
Gui
Peichun
P
Sohma
Yoshiro
Y
Meininger
Gerald A
GA
Davis
George E
GE
Braun
Andrew P
AP
Davis
Michael J
MJ
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D001160:Arterioles / Q000502:physiology*; D002478:Cells, Cultured; D039081:Integrin alpha5beta1 / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology*; D008297:Male; D009130:Muscle, Smooth / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D039081:Integrin alpha5beta1; D024681:Potassium Channels, Calcium-Activated