TRPV4 Increases Cardiomyocyte Calcium Transients and Contributes to Cardiac Damage Following Ischemia-Reperfusion in Hearts of Aged Mice

Abstract

Transient Receptor Potential Vanilloid 4 (TRPV4) is an osmotically-activated cation channel, and expression is increased in cardiomyocytes of Aged mice. The goal of this investigation was to determine the role of TRPV4 in calcium handling following hypoosmotic stress and in cardiac function following ischemia-reperfusion (I-R). Hypoosmotic stress (250 mOsm pretreatment) induced an increase in action potential-induced calcium transient amplitude (fluo-4) in cardiomyocytes isolated from Aged (24-26 month) mice. This effect was prevented by TRPV4 inhibition with HC067047 (1μM), and was absent in cardiomyocytes from Young (3-6 month) mice. The elevation in calcium transients in Aged associated with an increase in ryanodine receptor-mediated calcium sparks (3.4±0.7 sparks/s/100μm hypoosmotic versus 1.1±0.3 control, P<0.05). Cardiac contractile function was examined in Langendorff-perfused hearts prior to and following global I-R (45 minutes ischemia, two hours reperfusion), and hearts of Aged responded to I-R with an initial increase in contractile function during reperfusion (ΔdP/dtMax: gain of 674±226 mmHg/s from baseline). The enhanced contractility during reperfusion of Aged was prevented by TRPV4 inhibition with HC067047 (ΔdP/dtMax: loss of 290±102 mmHg/s from baseline) and was absent in hearts of Young (ΔdP/dtMax: loss of 621±400 mmHg/s from baseline). Following two hours of reperfusion, metabolically active tissue was assessed using triphenyltetrazolium chloride. In hearts of Aged, TRPV4 inhibition with HC067047 decreased the percentage of damaged tissue compared to untreated conditions (7±3% HC067047 versus 21±5% untreated, P<0.05), revealing a potential pathological role of TRPV4 in cardiomyocyte viability. Taken together, our data suggest that while TRPV4 may increase calcium transients and contractile function, it also contributes to cardiomyocyte damage following I-R.