Aggarwal R, Boyden P A
Department of Pharmacology, Columbia College of Physicians and Surgeons, New York, NY, USA.
J Cardiovasc Electrophysiol. 1996 Jan;7(1):20-35. doi: 10.1111/j.1540-8167.1996.tb00457.x.
The pharmacologic responses of macroscopic L-type calcium channel currents to the dihydropyridine agonist, Bay K 8644, and beta-adrenergic receptor stimulation by isoproterenol were studied in myocytes enzymatically dissociated from the epicardial border zone of the arrhythmic 5-day infarcted canine heart (IZs). Calcium currents were recorded at 36 degrees to 37 degrees C using the whole cell, patch clamp method and elicited by applying step depolarizations from a holding potential of -40 mV to various test potentials for 250-msec duration at 8-second intervals. A Cs+ -rich and 10 mM EGTA-containing pipette solution and a Na+ -and K+ -free external solutions were used to isolate calcium currents from other contaminating currents. During control, peak ICa,L density was found to be significantly less in IZs (4.0 +/- 1.1 pA/pF) than in myocytes dispersed from the epicardium of the normal noninfarcted heart (NZs; 6.5 +/- 1.8 pA/pF). Bay K 8644 (1 micro M) significantly increased peak ICa,L density 3.5-fold above control levels in both NZs (to 22.5 +/- 6.2 pA/pF; n = 7) and IZs (to 12.8 +/- 3.0 pA/pF; n = 5), yet peak ICa,L density in the presence of drug was significantly less in IZs than NZs. The effects of Bay K 8644 on kinetics of current decay and steady-state inactivation relations of peak ICa,L were similar in the two cell types. In contrast, the response of peak L-type current density to isoproterenol (1 micro M) was significantly diminished in IZs compared to NZs regardless of whether Ba2+ or Ca2+ ions carried the current. Thus, these results indicate an altered responsiveness to beta-adrenergic stimulation in cells that survive in the infarcted heart. Furthermore, application of forskolin (1 micro M and 10 micro M) or intracellular cAMP (200 micro M), agents known to act downstream of the beta-receptor, also produced a smaller increase in peak IBa density in IZs versus NZs, suggesting that multiple defects exist in the beta-adrenergic signaling pathway of IZs. In conclusion, these studies illustrate that reduced macroscopic calcium currents of cells in the infarcted heart exhibit an altered pharmacologic profile that has important implications in the development of drugs for the diseased heart.
在从梗死5天的犬心律失常心脏的心外膜边缘区（IZs）酶解分离的心肌细胞中，研究了宏观L型钙通道电流对二氢吡啶激动剂Bay K 8644的药理反应以及异丙肾上腺素对β-肾上腺素能受体的刺激作用。使用全细胞膜片钳方法在36℃至37℃记录钙电流，通过以-40mV的钳制电位施加阶跃去极化至各种测试电位，持续250毫秒，间隔8秒来诱发钙电流。使用富含Cs +和含10mM EGTA的微电极溶液以及无Na +和K +的外部溶液来从其他污染电流中分离钙电流。在对照期间，发现IZs中的峰值L型钙电流密度（4.0±1.1pA/pF）明显低于从正常非梗死心脏的心外膜分散的心肌细胞（NZs；6.5±1.8pA/pF）。Bay K 8644（1μM）使NZs（至22.5±6.2pA/pF；n = 7）和IZs（至12.8±3.0pA/pF；n = 5）的峰值L型钙电流密度比对照水平显著增加3.5倍，但药物存在时IZs中的峰值L型钙电流密度仍显著低于NZs。Bay K 8644对电流衰减动力学和峰值L型钙电流的稳态失活关系的影响在两种细胞类型中相似。相反，无论电流由Ba2 +还是Ca2 +携带，与NZs相比，IZs中峰值L型电流密度对异丙肾上腺素（1μM）的反应都显著减弱。因此，这些结果表明梗死心脏中存活细胞对β-肾上腺素能刺激的反应性发生了改变。此外，应用福斯可林（1μM和10μM）或细胞内cAMP（200μM），已知在β受体下游起作用的试剂，与NZs相比，IZs中峰值Ba电流密度的增加也较小，这表明IZs的β-肾上腺素能信号通路存在多个缺陷。总之，这些研究表明梗死心脏中细胞的宏观钙电流减少表现出改变的药理特征，这对患病心脏药物的开发具有重要意义。
