Effects of Three Different Ca(2+) Pump ATPase Inhibitors on Evoked Contractions in Rabbit Aorta and Activities of Ca(2+) Pump ATPases in Porcine Aorta.

Using vascular smooth muscle, we describe the actions of three pharmacological tools, cyclopiazonic acid (CPA), thapsigargin (TG) and 2,5-di-(tert-butyl)-1,4-benzohydroquinone (tBHQ), which are presumed to act as selective inhibitors of the sarco-endoplasmic reticulum Ca2+-ATPases (SERCAs). In porcine aortic smooth muscle microsomes two Ca2+-ATPase activities have been described, one vanadate-sensitive and one vanadate-resistant, representing the Ca2+-ATPase activities of the plasma membrane and SERCAs, respectively. In agreement, CPA, TG and tBHQ, in the concentration range 0.1 muM to 0.1 mM, dose-dependently inhibit the Ca2+-ATPase activity only in the vanadate-resistant microsomes. However, 0.1 mM tBHQ also significantly inhibited the Ca2+-ATPase activity of vanadate-sensitive microsomes. In rabbit aortic rings, all three SERCA inhibitors produced a dose-dependant inhibition of contractions evoked by 20 mM caffeine or 1 muM phenylephrine (PE) in a Ca2+-free physiological solution. However, in PE-contracted rings, tBHQ (greater than or equal to 30 muM) also significantly inhibited the ability of cromakalim to induce relaxation. In conclusion, the data suggest that CPA, TG and tBHQ can all act as selective SERCA inhibitors in both porcine and rabbit aortic smooth muscle. However, in contrast to CPA and TG, high concentrations of tBHQ can exhibit some nonspecific effects, which include inhibition of the plasma membrane Ca2+-ATPase and possibly K+ channels regulated by cromakalim. (C) 2000 Elsevier Science Inc. All rights reserved.