Hove-Madsen L, Llach A, Tort L
Department of Physiology, Cell Biology and Immunology, Faculty of Science, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
Am J Physiol Regul Integr Comp Physiol. 2000 Nov;279(5):R1856-64. doi: 10.1152/ajpregu.2000.279.5.R1856.
We have used the whole cell configuration of the patch-clamp technique to measure sarcolemmal Ca(2+) transport by the Na(+)/Ca(2+) exchanger (NCX) and its contribution to the activation and relaxation of contraction in trout atrial myocytes. In contrast to mammals, cell shortening continued, increasing at membrane potentials above 0 mV in trout atrial myocytes. Furthermore, 5 microM nifedipine abolished L-type Ca(2+) current (I(Ca)) but only reduced cell shortening and the Ca(2+) carried by the tail current to 66 +/- 5 and 67 +/- 6% of the control value. Lowering of the pipette Na(+) concentration from 16 to 10 or 0 mM reduced Ca(2+) extrusion from the cell from 2.5 +/- 0.2 to 1.0 +/- 0.2 and 0.5 +/- 0.06 amol/pF. With 20 microM exchanger inhibitory peptide (XIP) in the patch pipette Ca(2+) extrusion 20 min after patch break was 39 +/- 8% of its initial value. With 16, 10, and 0 mM Na(+) in the pipette, the sarcoplasmic reticulum (SR) Ca(2+) content was 47 +/- 4, 29 +/- 6, and 10 +/- 3 amol/pF, respectively. Removal of Na(+) from or inclusion of 20 microM XIP in the pipette gradually eliminated the SR Ca(2+) content. Whereas I(Ca) was the same at -10 or +10 mV, Ca(2+) extrusion from the cell and the SR Ca(2+) content at -10 mV were 65 +/- 7 and 80 +/- 4% of that at +10 mV. The relative amount of Ca(2+) extruded by the NCX (about 55%) and taken up by the SR (about 45%) was, however, similar with depolarizations to -10 and +10 mV. We conclude that modulation of the NCX activity critically determines Ca(2+) entry and cell shortening in trout atrial myocytes. This is due to both an alteration of the transsarcolemmal Ca(2+) transport and a modulation of the SR Ca(2+) content.
我们采用膜片钳技术的全细胞模式来测量钠钙交换体（NCX）介导的肌膜钙转运，并研究其对虹鳟心房肌细胞收缩激活和舒张的贡献。与哺乳动物不同，虹鳟心房肌细胞在膜电位高于0 mV时细胞缩短仍会持续增加。此外，5 μM硝苯地平可消除L型钙电流（I(Ca)），但仅将细胞缩短及尾电流携带的钙减少至对照值的66±5%和67±6%。将微管内钠离子浓度从16 mM降至10 mM或0 mM，可使细胞钙外排量从2.5±0.2降至1.0±0.2和0.5±0.06 amol/pF。膜片钳微管内加入20 μM交换体抑制肽（XIP）后，膜片破裂20分钟时的钙外排量为初始值的39±8%。微管内钠离子浓度为16 mM、10 mM和0 mM时，肌浆网（SR）钙含量分别为47±4、29±6和10±3 amol/pF。微管内去除钠离子或加入20 μM XIP可逐渐消除SR钙含量。尽管在-10 mV和+10 mV时I(Ca)相同，但-10 mV时细胞钙外排量和SR钙含量分别为+10 mV时的65±7%和80±4%。然而，NCX介导的钙外排相对量（约55%）和SR摄取的钙相对量（约45%）在去极化至-10 mV和+10 mV时相似。我们得出结论，NCX活性的调节对虹鳟心房肌细胞的钙内流和细胞缩短起关键作用。这是由于跨肌膜钙转运的改变以及SR钙含量的调节所致。
