The effects of cyclopiazonic acid on intracellular Ca2+ in aortic smooth muscle cells from DOCA-hypertensive rats.
We tested the hypothesis that cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase, increases intracellular Ca2+ concentration ([Ca2+]) in aortic myocytes and that the increase in [Ca2+]i is higher in aortic cells from deoxycorticosterone acetate (DOCA)-hypertensive rats. Male Sprague-Dawley rats, 250-300 g, underwent uninephrectomy, received a silastic implant containing DOCA (200 mg/kg) and had free access to water supplemented with 1.0% NaCl and 0.2% KCl. Control rats were also uninephrectomized, received normal tap water, but no implant. Intracellular Ca2+ measurements were performed in aortic myocytes isolated from normotensive (Systolic blood pressure = 120 +/- 3 mmHg; body weight = 478 +/- 7 g, N = 7) and DOCA-hypertensive rats (195 +/- 10 mmHg; 358 +/- 16 g, N = 7). The effects of CPA on resting [Ca2+]i and on caffeine-induced increase in [Ca2+]i after [Ca2+]i depletion and reloading were compared in aortic cells from DOCA and normotensive rats. The phasic increase in [Ca2+]i induced by 20 mM caffeine in Ca(2+)-free buffer was significantly higher in DOCA aortic cells (329 +/- 36 nM, N = 5) compared to that in normotensive cells (249 +/- 16 nM, N = 7, P < 0.05). CPA (3 microM) inhibited caffeine-induced increases in [Ca2+]i in both groups. When the cells were placed in normal buffer (1.6 mM Ca2+, loading period), after treatment with Ca(2+)-free buffer (depletion period), an increase in [Ca2+]i was observed in DOCA aortic cells (45 +/- 11 nM, N = 5) while no changes were observed in normotensive cells. CPA (3 microM) potentiated the increase in [Ca2+]i (122 +/- 30 nM, N = 5) observed in DOCA cells during the loading period while only a modest increase in [Ca2+]i (23 +/- 10 nM, N = 5) was observed in normotensive cells. CPA-induced increase in [Ca2+]i did not occur in the absence of extracellular Ca2+ or in the presence of nifedipine. These data show that CPA induces Ca2+ influx in aorta from both normotensive and DOCA-hypertensive rats. However, the increase in [Ca2+]i is higher in DOCA aortic cells possibly due to an impairment in the mechanisms that control [Ca2+]i. The large increase in [Ca2+]i in response to caffeine in DOCA cells probably reflects a greater storage of Ca2+ in the SR.
Tostes
R C
RC
Department of Physiology, University of Michigan, Ann Arbor 48109-0622, USA. rtostes@usp.br
Wilde
D W
DW
Bendhack
L M
LM
Webb
R C
RC
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003900:Desoxycorticosterone / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006973:Hypertension / Q000139:chemically induced*; D007211:Indoles / Q000494:pharmacology*; D007424:Intracellular Fluid; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014665:Vasodilator Agents / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D000697:Central Nervous System Stimulants; D004791:Enzyme Inhibitors; D007211:Indoles; D014665:Vasodilator Agents; D002110:Caffeine; D003900:Desoxycorticosterone; D009543:Nifedipine; D002118:Calcium; C000543:cyclopiazonic acid