Gómez-Viquez Leticia, Guerrero-Serna Guadalupe, García Ubaldo, Guerrero-Hernández Agustín
Departamento de Bioquímica, CINVESTAV-IPN, México D.F., 07000, Mexico.
Biophys J. 2003 Jul;85(1):370-80. doi: 10.1016/S0006-3495(03)74481-6.
Thapsigargin-sensitive sarco/endoplasmic reticulum Ca(2+) pumps (SERCAs) are involved in maintaining and replenishing agonist-sensitive internal stores. Although it has been assumed that release channels act independently of SERCA pumps, there are data suggesting the opposite. Our aim was to study the relationship between SERCA pumps and the release channels in smooth muscle cells. To this end, we have rapidly blocked SERCA pumps with thapsigargin, to avoid depletion of the internal Ca(2+) stores, and induced Ca(2+) release with either caffeine, to open ryanodine receptors, or acetylcholine, to open inositol 1,4,5-trisphosphate receptors. Blocking SERCA pumps produced smaller and slower agonist-induced Ca(2+) responses. We determined the Ca(2+) level of the internal stores both indirectly, measuring the frequency of spontaneous transient outward currents, and directly, using Mag-Fura-2, and demonstrated that the inhibition of SERCA pumps did not produce a reduction of the sarco/endoplasmic reticulum Ca(2+) levels to explain the decrease in the agonist-induced Ca(2+) responses. It appears that SERCA pumps are involved in sustaining agonist-induced Ca(2+) release by a mechanism that involves the modulation of Ca(2+) availability in the lumen of the internal stores.
毒胡萝卜素敏感的肌浆网/内质网Ca(2+)泵（SERCAs）参与维持和补充激动剂敏感的内部钙库。尽管一直认为释放通道独立于SERCA泵发挥作用，但有数据表明情况恰恰相反。我们的目的是研究平滑肌细胞中SERCA泵与释放通道之间的关系。为此，我们用毒胡萝卜素快速阻断SERCA泵，以避免内部Ca(2+)库耗竭，并用咖啡因（以打开兰尼碱受体）或乙酰胆碱（以打开肌醇1,4,5-三磷酸受体）诱导Ca(2+)释放。阻断SERCA泵会使激动剂诱导的Ca(2+)反应变小且变慢。我们通过间接测量自发瞬态外向电流的频率以及直接使用Mag - Fura - 2来确定内部钙库的Ca(2+)水平，并证明抑制SERCA泵不会导致肌浆网/内质网Ca(2+)水平降低，无法解释激动剂诱导的Ca(2+)反应的减少。似乎SERCA泵通过一种涉及调节内部钙库腔中Ca(2+)可用性的机制参与维持激动剂诱导的Ca(2+)释放。
