Evoked tensions in rabbit aorta by emptying intracellular Ca2+ stores with cyclopiazonic acid, thapsigargin, and ryanodine.
OBJECTIVE
To study the increase of plasma membrane Ca2+ permeability in response to depletion of intracellular Ca2+ stores.


METHODS
In Ca(2+)-free medium, 2 selective inhibitors of sarcoplasmic reticulum (SR) Ca2+ pump ATPase, cyclopiazonic acid (CPA) and thapsigargin (Tha), and an activator of Ca(2+)-induced Ca2+ release channel (CICR), ryanodine (Rya), depleted intracellular Ca2+ stores sensitive to both caffeine and phenylephrine in rabbit aortic rings and caused sustained tensions when Ca2+ reintroduction. These tensions were taken as the increase of plasma Ca2+ permeability by depletion of intracellular Ca2+ stores.


RESULTS
The extracellular Ca(2+)-dependent tensions caused by Tha and Rya 3 mumol.L(-1) and CPA 30 mumol.L(-1) were 0.94, 1.1, and 0.14 g, respectively, and the tension caused by Rya was not inhibited by CPA.


CONCLUSIONS
(a) Besides the depletion of intracellular Ca2+ stores, an activated state of Ca2+ release channels in SR may also mediate the activation of Ca2+ influx from plasma membrane in rabbit aorta; (b) Rya needs caffeine to fully open CICR channel in SR.
Luo
D L
DL
Department of Pharmacology, Harbin Medical University, China.
Li
W H
WH
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002199:Capillary Permeability / Q000187:drug effects; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D007211:Indoles; D013729:Terpenes; D012433:Ryanodine; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid