Abstract 6024: Sirolimus Increases Outward KATP Current in Human Coronary Arterial Smooth Muscle Cells
Introduction: Sirolimus is widely used to prevent restenosis in drug-eluting stents. Although the antiproliferative and immunosuppressant effects of sirolimus are well established, little is known with regard to its effects on vasomotor tone. We have previously shown that sirolimus causes relaxation of isolated human arteries and that this response is inhibited by glyburide, a potent and selective KATP channel blocker, suggesting that sirolimus-induced relaxation is mediated via the opening of KATP channels.
Hypothesis: In this study, we directly tested the hypothesis that sirolimus increases outward potassium current via KATP channels in human vascular smooth muscle cells.
Methods: Potassium currents were recorded in cultured human coronary artery smooth muscle cells by using the whole-cell patch clamp technique in voltage-clamp mode.
Results: Outward currents consistent with activation of KATP channels were recorded (peak current density = 57 ± 3 pA/pF; n=14). These currents were nearly abolished by glyburide (10−5 M) and by ATP (3 mM) (peak current density = 9 ± 2 pA/pF and 7 ± 3 pA/pF for glyburide and ATP, respectively; p<0.05 vs control), whereas iberiotoxin (10−6 M) had no effect (peak current density = 59 ± 9 pA/pF; p>0.05 vs control). In the presence of sirolimus (10−7 M) the I–V curve was shifted to the left and peak current density was increased to 168 ± 9 pA/pF (n=14; p<0.05). The effect of sirolimus was completely reversible following washout. Sirolimus mimicked the effect of the selective KATP channel opener, aprikalim (10−5 M), which also shifted the I–V curve to the left and increased peak current density to 245 ± 5 pA/pF (n=10; p<0.05). The effects of both sirolimus and aprikalim on the KATP current were markedly inhibited in the presence of glyburide (10−5 M) (p<0.05 vs in the absence of glyburide; n=10 –14).
Conclusions: These studies provide direct evidence for the opening of KATP channels by sirolimus in human coronary artery smooth muscle cells. Relaxation of vascular smooth muscle via KATP channel activation is a novel action of sirolimus that could contribute to its efficacy in drug-eluting stents.
This research has received full or partial funding support from the American Heart Association, AHA Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota & Wisconsin).