Abstract 491: Activation of Voltage-dependent L-type Calcium Channels and the Rho Kinase Pathway Are Involved in S1P-induced Vasoconstriction in Rat Juxtamedullary Afferent Arterioles
Sphingosine-1-phosphate (S1P) is an important regulator of resistance vessels and is implicated in pathological processes including diabetic nephropathy and acute kidney injury. Previous studies show that S1P causes marked vasoconstriction in preglomerular but not postglomerular microvessels, however, the intracellular signaling pathways underlying S1P-mediated vasoconstriction are undefined. We postulated that S1P-mediated afferent arteriolar (AA) vasoconstriction involves activation of voltage-dependent L-type Ca2+ channels (L-VDCC) and the rho kinase pathway. Studies were conducted in vitro using the blood-perfused juxtamedullary nephron preparation. Superfusion of S1P (n=6) evoked concentration-dependent AA vasoconstriction. Control diameter averaged 13.8±0.9 μm and declined to 95±2, 85±4, 75±6, 60±5 and 46±5% of control diameter in response to S1P (from 10-9 to 10-5 M), respectively. Superfusion with nifedipine (10-6 M, n=6), a L-VDCC inhibitor, increased basal diameter by 39±18% (p<0.05) and significantly attenuated the S1P-induced vasoconstriction. S1P reduced AA diameter to 99±1, 98±1, 90±3, 79±3 and 52±5% of control (p<0.05 vs. S1P alone at 10-8 to 10-6 M) during nifedipine treatment. Superfusion with the rho kinase inhibitor, Y27632 (10-5 M, n=6), increased diameter by 60±12% and inhibited S1P-induced vasoconstriction. AA diameter averaged 103±1, 101±1, 93±3, 72±9 and 56±10% of control in response to increasing concentrations of S1P (p<0.05 vs. S1P alone at 10-9 to 10-7 M). In contrast, S1P-induced vasoconstriction was unaltered by Ca2+ store depletion using the Ca2+-ATPase inhibitors, thapsigargin (Tg) and cyclopiazonic acid (CPA). Although Tg (10-6 M, n=4) increased diameter by 38±16%, the S1P-induced vasoconstrictor profile was not different from that without Tg. AA declined to 99±3, 95±5, 85±10, 60±13 and 32±8% (p>0.05), respectively. Similar results were obtained with CPA (10-5 M, n=6). S1P reduced diameter to 97±2, 93±2, 75±5, 53±6 and 36±5% of the control (p>0.05), respectively, suggesting that mobilization of intracellular Ca2+ store is not required for S1P-induced vasoconstriction. Overall, these data indicate that both L-VDCC and rho kinase pathways contribute to S1P-mediated AA vasoconstriction.
- © 2012 by American Heart Association, Inc.