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Address correspondence to Clive M. Baumgarten, Department of Physiology, Medical College of Virginia, Box 980551 Richmond, VA 23298-0551. Fax: (804) 828-7382; email: clive.baumgarten{at}vcu.edu
Osmotic swelling of cardiac myocytes and other types of cells activates an outwardly rectifying, tamoxifen-sensitive Cl- current, ICl,swell, but it is unclear whether Cl- currents also are activated by direct mechanical stretch. We tested whether specific stretch of ß1-integrin activates a Cl- current in rabbit left ventricular myocytes. Paramagnetic beads (4.5-µm diameter) coated with mAb to ß1-integrin were applied to the surface of myocytes and pulled upward with an electromagnet while recording whole-cell current. In solutions designed to isolate anion currents, ß1-integrin stretch elicited an outwardly rectifying Cl- current with biophysical and pharmacological properties similar to those of ICl,swell. Stretch-activated Cl- current activated slowly (t1/2 = 3.5 ± 0.1 min), partially inactivated at positive voltages, reversed near ECl, and was blocked by 10 µM tamoxifen. When stretch was terminated, 64 ± 8% of the stretch-induced current reversed within 10 min. Mechanotransduction involved protein tyrosine kinase. Genistein (100 µM), a protein tyrosine kinase inhibitor previously shown to suppress ICl,swell in myocytes, inhibited stretch-activated Cl- current by 62 ± 6% during continued stretch. Because focal adhesion kinase and Src are known to be activated by cell swelling, mechanical stretch, and clustering of integrins, we tested whether these tyrosine kinases mediated the response to ß1-integrin stretch. PP2 (10 µM), a selective blocker of focal adhesion kinase and Src, fully inhibited the stretch-activated Cl- current as well as part of the background Cl- current, whereas its inactive analogue PP3 (10 µM) had no significant effect. In addition to activating Cl- current, stretch of ß1-integrin also appeared to activate a nonselective cation current and to suppress IK1. Integrins are the primary mechanical link between the extracellular matrix and cytoskeleton. The present results suggest that integrin stretch may contribute to mechano-electric feedback in heart, modulate electrical activity, and influence the propensity for arrhythmogenesis.
Key Words: stretch-activated channels • swelling-activated channels • mechano-electric feedback • protein tyrosine kinase • arrhythmia
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