Cardiac mast cell degranulation mediates ET-1-induced cardioprotection in a rat model of myocardial ischaemia

Sarah K Walsh1, Kathleen A Kane2, Cherry L Wainwright1. 1The Robert Gordon University, Aberdeen, 2University of Strathclyde, Glasgow.

Exogenous endothelin-1 (ET-1) has been shown to have an antiarrhythmic effect when administered prior to myocardial ischaemia (Sharif et al., 1998). The exact mechanism by which ET-1 is antiarrhythmic remains elusive. ET-1 has been shown to induce degranulation of rat cardiac mast cells (MC) (Murray et al., 2004) and, since infusion of compound 48/80 (CMP 48/80; an MC degranulator) prior to coronary occlusion is also antiarrhythmic (Parikh et al., 1997), it is possible that ET-1 induced MC degranulation prior to ischaemia may be a mechanism underlying the antiarrhythmic effect of ET-1. The present studies were performed to test this hypothesis.

Male Sprague Dawley rats (300-400g) were anaesthetized with sodium pentobarbitone (60mg kg-1 i.p.), the right jugular vein cannulated for drug and anaesthetic (3-6mg kg-1 i.v. as required) administration and the heart prepared for coronary artery occlusion (CAO). After 15 min stabilisation vehicle (saline) or the MC stabiliser disodium chromoglycate (DSCG; 20mg kg-1 hr-1), was infused for 25 min prior to a bolus dose of either saline (n=12 and 8 for saline/DSCG infusion, respectively), ET-1 (1.6nmol kg-1, n=11 and 8), or CMP 48/80 (50μg kg-1, n=8 and 8). 5 min later CAO was induced for 30-min. DSCG infusion was terminated immediately prior to CAO and saline infusion continued for the period of ischaemia. Mean arterial blood pressure (MABP) was recorded via a carotid cannula, and heart rate (HR) measured from an ECG. The appearance of ventricular premature beats (VPBs), ventricular tachycardia (VT), and ventricular fibrillation (VF), was monitored. After 30 min CAO, hearts were removed and used for histological analysis to determine the incidence of MC degranulation. Sham groups were performed to determine the effects of the drugs alone on MC degranulation. Data are expressed as mean ± s.e.m and compared using either an ANOVA with Dunnett’s post-hoc test, two-way ANOVA with Bonferroni post-hoc test, or a Student’s T-test. The incidence of VT, VF, and mortality, was compared using Fisher’s exact test.

ET-1 and CMP 48/80 induced a transient decrease in MABP prior to ischaemia (94±9mmHg vs. 126±4mmHg; p<0.01 and 63±1mmHg vs. 126±2mmHg; p<0.001, respectively). ET-1 and CMP 48/80 both reduced the total number of VPBs (510±104 and 860±184, respectively; vs. 1959±240 in controls; p<0.001) and the incidence of VF (36% and 25%, respectively vs. 83%; p<0.05). The antiarrhythmic effects of both treatments were abolished by DSCG (50% and 75% VF, respectively). Ischaemia induced MC degranulation compared to sham controls (57±4% vs. 36±3%; p<0.001). ET-1 and CMP 48/80 induced MC degranulation in sham animals (63±6% and 68±7%, respectively; vs. 36±3%; p<0.001) and CMP 48/80 also increased degranulation during ischaemia (73±1% vs. 57±4%; p<0.05). These results demonstrate that both ET-1 and CMP 48/80 may mediate their anti-arrhythmic effect via MC degranulation prior to ischaemia.

Parikh et al., (1997) J. Cardiovasc. Pharmacol. 30, 49-156.
Sharif et al., (1998) Cardiovasc. Res. 39, 625-632.

SKW was supported by an RDI studentship from The Robert Gordon University