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Owen Jeffries, Mary K. McGahon, Peter Bankhead, Maria Manfredi Lozano, C. Norman Scholfield, Tim M. Curtis, J. Graham McGeown; cAMP/PKA-Dependent Increases in Ca Sparks, Oscillations and SR Ca Stores in Retinal Arteriolar Myocytes after Exposure to Vasopressin. Invest. Ophthalmol. Vis. Sci. 2010;51(3):1591-1598. doi: 10.1167/iovs.09-4401.
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© 2016 Association for Research in Vision and Ophthalmology.
To investigate the effects of arginine vasopressin (AVP) on Ca2+ sparks and oscillations and on sarcoplasmic reticulum (SR) Ca2+ content in retinal arteriolar myocytes.
Fluo-4-loaded smooth muscle in intact segments of freshly isolated porcine retinal arteriole was imaged by confocal laser microscopy. SR Ca2+ store content was assessed by recording caffeine-induced Ca2+ transients with microfluorimetry and fura-2.
The frequencies of Ca2+ sparks and oscillations were increased both during exposure to, and 10 minutes after washout of AVP (10 nM). Caffeine transients were increased in amplitude 10 and 90 minutes after a 3-minute application of AVP. Both AVP-induced Ca2+ transients and the enhancement of caffeine responses after AVP washout were inhibited by SR 49059, a V1a receptor blocker. Forskolin, an activator of adenylyl cyclase, also persistently enhanced caffeine transients. Rp-8-HA-cAMPS, a membrane-permeant PKA inhibitor, prevented enhancement of caffeine transients by both AVP and forskolin. Forskolin, but not AVP, produced a reversible, Rp-8-HA-cAMPS insensitive reduction in basal [Ca2+]i.
AVP activates a cAMP/PKA-dependent pathway via V1a receptors in retinal arteriolar smooth muscle. This effect persistently increases SR Ca2+ loading, upregulating Ca2+ sparks and oscillations, and may favor prolonged agonist activity despite receptor desensitization.
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