Vila-Petroff M, Pérez G N, Alvarez B, Cingolani H E, Mattiazzi A
Centro de Investigaciones Cardiovasculares, Universidad Nacional de La Plata, Argentina.
Am J Physiol. 1996 Feb;270(2 Pt 2):H701-9. doi: 10.1152/ajpheart.1996.270.2.H701.
Experiments were performed in cat papillary muscles to explore the mechanisms by which alpha 1-adrenoceptor stimulation affects myocardial relaxation. Phenylephrine (PE; 10 microM) + atenolol (1 microM; n = 8 experiments) produced a negative lusitropic effect, i.e., a prolongation of half-relaxation time (t1/2; time to 50% relaxation) by 30 +/- 10% (P < 0.05) and a proportionally smaller increase in maximal velocity of relaxation (-T) than in maximal velocity of contraction (+T), which significantly increased the ratio +T/-T. A similar increase in contractility, produced by increasing calcium, failed to significantly change t1/2 and +T/-T. PE-induced negative lusitropic effect was significantly inhibited by two protein kinase C (PKC) inhibitors, staurosporine (0.1 microM) and chelerythrine (10 microM). PE also increased intracellular pH by 0.18 +/- 0.05 pH units (P < 0.05, n = 4), as measured by the fluorescent dye 2'-7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Intracellular alkalosis and the negative lusitropic effect of PE were prevented by the Na+/H+ exchanger inhibitor ethylisopropylamiloride (10 microM). No significant changes in calcium myofilament sensitivity and maximal tension were detected in trabeculae treated with PE either before or after chemical skinning. These results indicate that a Na+/H+ exchanger-induced intracellular alkalosis, possibly mediated by PKC activation, may fully account for the negative lusitropism of alpha 1-adrenoceptor stimulation.
在猫乳头肌上进行实验，以探究α1肾上腺素能受体刺激影响心肌舒张的机制。苯肾上腺素（PE；10微摩尔）+阿替洛尔（1微摩尔；n = 8次实验）产生负性变时性效应，即半舒张时间（t1/2；达到50%舒张的时间）延长30±10%（P < 0.05），舒张最大速度（-T）的增加比例小于收缩最大速度（+T），这显著增加了+T/-T比值。通过增加钙产生的类似收缩性增加，未能显著改变t1/2和+T/-T。两种蛋白激酶C（PKC）抑制剂，星形孢菌素（0.1微摩尔）和白屈菜红碱（10微摩尔），显著抑制了PE诱导的负性变时性效应。通过荧光染料2'-7'-双（2-羧乙基）-5（6）-羧基荧光素测量，PE还使细胞内pH值升高0.18±0.05个pH单位（P < 0.05，n = 4）。Na+/H+交换体抑制剂乙基异丙基氨氯地平（10微摩尔）可预防细胞内碱化和PE的负性变时性效应。在用PE处理的小梁中，无论是化学去表皮前还是去表皮后，均未检测到钙肌丝敏感性和最大张力的显著变化。这些结果表明，Na+/H+交换体诱导的细胞内碱化，可能由PKC激活介导，可能完全解释了α1肾上腺素能受体刺激的负性变时性作用。
