Abstract 15884: Arrhythmogenic Effect of Store-Operated Calcium Entry in Mouse Ventricular Myocytes
Background: Store operated Ca2+ entry (SOCE) has recently been found in myocytes isolated from fetal, neonatal, and diseased hearts. However, its existence, molecular nature and (patho)physiological relevance in normal adult hearts remain unclear.
Methods and Results: Cytosolic Ca2+ (Cai) was imaged in fluo-4-AM loaded ventricular myocytes isolated from adult mice (2-4 month old). Membrane potential was measured using the perforated patch-clamp technique. The existence of SOCE was demonstrated in cardiac myocytes treated with both caffeine (10 mM) and thapsigargin/CPA (F/F0 = 2.74 ± 0.73, n = 9) compared to thapsigargin/CPA only (F/F0 =1.73 ± 0.38, n = 9, p<0.05), suggesting the complete depletion of sarcoplasmic reticulum (SR) Ca is required for apparent SOCE activation. The SOCE was significantly reduced by pretreatment with anti-TRPC1, 3, and 6 antibodies ( to 25 ± 9%, 12 ± 3% and 8 ± 3% comparing to the control, n = 9, 8, 8, 37 respectively, p<0.05) as well as by gadolinium (Gd), a non-selective TRPC channel blocker (to 15 ± 5 %, n = 6, p<0.05), consistent with the notion that SOCE may be mediated by heteromultimeric TRPC channels. We then demonstrated SOCE may regulate spontaneous sarcoplasmic reticulum (SR) Ca release, Cai waves, and triggered activities. Elevating external Ca2+ concentration ([Ca]O, from 1mM to 4 mM) induced spontaneous Cai waves, which were suppressed by Gd, but not by the L-type Ca current (ICa,L) blocker nifedipine or the sodium-calcium exchanger blocker SEA0400. Both Ca overload and arachidonic acid (AA) overproduction were found during some pathological conditions, such as ischemia. We observed that AA (10 µM) and 1,2-Dioctanoyl-sn-glycerol (DOG) (10 µM), a membrane permeable analogue of diacylglycerol, increased Ca wave frequency by 75 ±15 %, n = 22, and 76 ± 17 %, n = 8 respectively, and by 196 ± 37 %, n = 15 in the presence of both, p<0.001. The SOCE currents enhanced by high [Ca]O and AA were recorded while ICa,L and K+ currents were minimized.
Conclusion: We have demonstrated SOCE, which is at least partially mediated by TRPC channels, exists in ventricular myocytes isolated from normal adult mice and is involved in spontaneous Ca waves and triggered activities, which may manifest cardiac arrhythmias under the ischemic condition.
- © 2011 by American Heart Association, Inc.