Store-operated Ca²⁺ entry modulates sarcoplasmic reticulum Ca²⁺ loading in neonatal rabbit cardiac ventricular myocytes

Abstract

Store-operated Ca2+ entry (SOCE), which is Ca2+ entry triggered by the depletion of intracellular Ca2+ stores, has been observed in many cell types, but only recently has it been suggested to occur in cardiomyocytes. In the present study, we have demonstrated SOCE-dependent sarcoplasmic reticulum (SR) Ca2+ loading (load(SR)) that was not altered by inhibition of L-type Ca2+ channels, reverse mode Na+/Ca2+ exchange (NCX), or nonselective cation channels. In contrast, lowering the extracellular [Ca2+] to 0 mM or adding either 0.5 mM Zn2+ or the putative store-operated channel (SOC) inhibitor SKF-96365 (100 microM) inhibited load(SR) at rest. Interestingly, inhibition of forward mode NCX with 30 microM KB-R7943 stimulated SOCE significantly and resulted in enhanced load(SR). In addition, manipulation of the extracellular and intracellular Na+ concentrations further demonstrated the modulatory role of NCX in SOCE-mediated SR Ca2+ loading. Although there is little knowledge of SOCE in cardiomyocytes, the present results suggest that this mechanism, together with NCX, may play an important role in SR Ca2+ homeostasis. The data reported herein also imply the presence of microdomains unique to the neonatal cardiomyocyte. These findings may be of particular importance during open heart surgery in neonates, in which uncontrolled SOCE could lead to SR Ca2+ overload and arrhythmogenesis.

STIM1/Orai1-mediated SOCE: current perspectives and potential roles in cardiac function and pathology

“…It should be noted, however, that Gd 3ϩ is a nonspecific cation channel inhibitor; therefore interpretation of results based on Gd 3ϩ need to be made with caution. Nevertheless, these data support earlier findings of Huang et al (36) who showed that in neonatal rabbit cardiomyocytes increased SR Ca 2ϩ content and resultant arrhythmic activity could be attenuated by SKF96365. In addition, TRPC channel expression and SOCE have both been shown to occur in pacemaker cells such as those of the sinoatrial node (41,105).…”

SR Ca2+ refilling upon depletion and SR Ca2+ uptake rates during development in rabbit ventricular myocytes

“…It has been suggested that neonatal mammalian ventricular myocytes have a relatively sparse and immature SR compared with that in adults (11,25), but recent studies indicate that a prominent SR Ca 2ϩ accumulation can take place in neonatal myocytes (12,13,21). Here we have attempted to identify, quantify, and compare the mechanisms contributing to load SR in neonatal and adult hearts.…”

“…The Simon Fraser University Animal Care Committee approved the use of animals and the experimental protocol used in this study in accordance with CCAC regulations. Ventricular myocytes were isolated from the hearts of New Zealand White rabbits (of either sex) from four distinct age groups, 3 (3d), 10 (10d), 20 (20d), and 56 (56d) days postpartum, by methods previously described (12,13,17).…”

“…Whole cell amphotericin-perforated voltage-clamp technique was used at room temperature as described previously (12,13,17 …”

“…5D for the different age groups. The calculation of the contribution of NifϩKB-Rinsensitive load SR is predicated on two observations: 1) steady state in control solution was achieved at ϳ10th depolarization (ϳ50 s) and 2) NifϩKB-R-insensitive load SR is linear with time for up to 100 s (13). Therefore the contribution of NifϩKB-R-insensitive load SR relative to Con is derived from the assumption that its loading is the half-value of NifϩKB-R-insensitive load SR (ϳ100 s).…”