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Heart, Lung and Circulation Abstracts S2412008;17S:S219–S241

545Systemic Urotensin II Infusion Induces Diastolic Dys-function in Normal Rat Heart Independent of BloodPressure: Contribution of Rho Kinase-Mediated Extracel-lular Matrix Production

Lavinia Tran 1,∗, Andrew Kompa 1, William Kemp 1, Arin-taya Phrommintikul 2, Bing Wang 1, Henry Krum 1

1 Monash University, Prahran, Victoria, Australia; 2 ChiangMai University, Chiang Mai, Thailand

Objective: Urotensin II (UII), a potent vaso-active pep-tide, may play a pathological role in hypertension andcardiac remodelling; however its contribution to diastolicdysfunction has not been explored. This study examinesthe effects of chronic UII infusion on blood pressure (BP),cardiac structure and function. Rho kinase (ROCK) wasinvestigated as a signalling pathway for UII in vitro.Methods: Rats were intravenously infused with UII at2.0 �g/(kg h) (low dose) or 5.2 �g/(kg h) (high dose) orvehicle (saline) for 4 weeks. Echocardiograms and haemo-dynamic analysis was used to assess cardiac function.Immunohistochemistry and Real-Time PCR examinedexpression of left ventricular (LV) collagen, Neonatal car-diac fibroblasts (NCF) over-expressing the UII receptorwere stimulated with UII (10−7 M) in the presence andabsence of the ROCK inhibitor GSK576371 (10−7 TO10−5 M), and collagen synthesis was determined using[Roii(tiN(s4Citmbt

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546The Role of L- and T-Channels in the Large and Microvas-culature

Christine Ball 1,∗, David Saint 2, John Beltrame 1, DavidWilson 2

1 Cardiology Unit, The Queen Elizabeth Hospital, Adelaide,Australia; 2 Discipline of Physiology, School of Molecular andBiomedical Sciences, The University of Adelaide, Adelaide, Aus-tralia

Background: Our previous studies have demonstratedincremental clinical benefits of T-type Ca2+ channelblockers (CCBs) over conventional L-type CCBs inmicrovascular disorders. Furthermore, we have shownthat combined L- and T-type CCBs are more effective atattenuating agonist-mediated microvascular constriction.The aims of this study were to directly examine the con-tribution of the voltage-sensitive Ca2+ channels in thisheterogeneous response and explore its underlying mech-anism.Methods: Contractile-responses to K+-mediated depolar-ization in the presence of L-type CCBs (verapamil andnifedipine) or combined L- and T-type CCBs (efonidip-ine and mibefradil) were assessed in rat large (aorta) andsmall (mesenteric) vessels using wire myography. mRNAexpression of L- and T-channel expression in rat aorta andmesenteric arteries was determined to ascertain whethertCReCmiwTbCmapdpd

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3H]-proline incorporation.esults: UII infusion had no effect on systemic BPr cardiac hypertrophy. Both doses of UII significantly

mpaired diastolic function demonstrated by Dopplerndices, E-wave deceleration time and MV annulus E′/A′Table). Collagen I deposition and gene expression inhe LV was significantly increased with high dose UIInfusion compared to vehicle (Table). Stimulation of

CF with UII significantly increased collagen turnoverp < 0.05). GSK576371 dose-dependently attenuated UII-timulated collagen synthesis in NCF (31.5 ± 4.3%, 10−7 M;9.7 ± 5.0%, 10−6 M; 57.6 ± 6.1%, 10−5 M, p < 0.001).onclusion: UII infusion produces diastolic dysfunction

ndependent of effects on systemic BP and cardiac hyper-rophy. Increased collagen deposition and gene expression

ay explain changes in LV diastolic function. ROCK maye involved in pathogenic LV remodelling leading to dias-

olic dysfunction.Vehicle Low dose UII High dose UII

-wave deceleration time (DT, ms) 56.7 ± 3.3 92.5 ± 4.53** 118.0 ± 21.5*

V annulus (MVa) E′/A′ (ms) 2.01 ± 0.19 1.04 ± 0.05* 1.04 ± 0.25**

ollagen I protein in LV (% area) 0.71 ± 0.13 1.22 ± 0.15# 2.18 ± 0.29***

otal Collagen protein in LV (%area)

2.24 ± 0.26 2.52 ± 0.30 4.63 ± 0.50*

rocollagen-�1 gene expression(ratio of collagen I: 18s)

0.80 ± 0.09 1.12 ± 0.06 1.39 ± 0.16*

ata presented as mean ± S.E.M., *p < 0.05, **p < 0.01, ***p < 0.001 vs. vehi-le, #p < 0.05 vs. high dose UII.

oi:10.1016/j.hlc.2008.05.599

his could account for the heterogeneous response toCBs.esults: In microvessels, K+ responses were moreffectively inhibited by the combined L- and T-typeCB than L-type CCBs (K+ Emax: efonidipine = 2 ± 1%*,ibefradil = 3 ± 2%*, for both verapamil and nifedip-

ne = 12 ± 1%; *p < 0.05 T- vs. L-). In contrast, all the CCBsere equally effective at attenuating aortic constriction.here was no difference in L- or T-channel expressionetween small and large vessels.onclusion: Combined L- and T-type CCBs are muchore effective at inhibiting contraction in small resistance

rteries than conventional L-type CCBs. The identifiedharmacodynamic heterogeneity is not consistent withifferential Ca2+ channel mRNA expression. Ongoingatch clamp studies are aimed at identifying Ca2+ channelensity.

oi:10.1016/j.hlc.2008.05.600