cAMP/PKA-Dependent Increases in Ca Sparks, Oscillations and SR Ca Stores in Retinal Arteriolar Myocytes after Exposure to Vasopressin

Abstract

PURPOSE.To investigate the effects of arginine vasopressin (AVP) on Ca 2ϩ sparks and oscillations and on sarcoplasmic reticulum (SR) Ca 2ϩ content in retinal arteriolar myocytes. METHODS.Fluo-4-loaded smooth muscle in intact segments of freshly isolated porcine retinal arteriole was imaged by confocal laser microscopy. SR Ca 2ϩ store content was assessed by recording caffeine-induced Ca 2ϩ transients with microfluorimetry and fura-2. RESULTS. The frequencies of Ca 2ϩ 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 Ca 2ϩ transients and the enhancement of caffeine responses after AVP washout were inhibited by SR 49059, a V 1a 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 [Ca 2ϩ ] i .CONCLUSIONS. AVP activates a cAMP/PKA-dependent pathway via V 1a receptors in retinal arteriolar smooth muscle. This effect persistently increases SR Ca 2ϩ loading, upregulating Ca 2ϩ sparks and oscillations, and may favor prolonged agonist activity despite receptor desensitization. (Invest Ophthalmol Vis Sci. 2010;51:1591-1598

Endothelin 1 Stimulates Ca2+-Sparks and Oscillations in Retinal Arteriolar Myocytes via IP3R and RyR-Dependent Ca2+Release

“…24,33 Ca 2ϩ -oscillations can also be evoked in vascular smooth muscle by a range of other agonists. 34 We have reported similar behavior in porcine retinal arterioles exposed to arginine vasopressin (AVP), 21 although the resultant oscillations did not have the impressive rhythmicity so obvious in Et1 responses (Fig. 1).…”

“…For Ca 2ϩ -sparks, custom-designed software based on an à trous wavelet transform was used to automate detection and analysis, as previously described. 21 Spark amplitude was defined as the maximum increase in ⌬F/F 0 for a 5-pixelwide region of interest centered on the point of maximum fluorescence. The full duration at half-maximal fluorescence and the full width at half-maximal fluorescence were also measured for each event.…”

“…We have previously reported that high-speed Ca 2ϩ -imaging reveals brief, localized subcellular Ca 2ϩ -signals known as Ca 2ϩ -sparks in both rat and pig retinal arterioles 20,21 ( Fig. 2A).…”

PICK1/calcineurin suppress ASIC1-mediated Ca2+ entry in rat pulmonary arterial smooth muscle cells

“…Although this will decrease [Ca 2ϩ ] i and lead to smooth muscle relaxation, increasing the Ca 2ϩ load of the SR will also lead to faster turn around and increased release of Ca 2ϩ from the stores upon subsequent and/or continuous activation. Indeed, PKA increases Ca 2ϩ -spark frequency mediated by SR ryanodine receptor channels (RyR) (18,30,47). It is possible that PKA not only regulates SR Ca 2ϩ through SERCA and RyR channels but also by activating the store-operated channels responsible for replenishing the SR. PKA has recently been shown to activate the heteromeric Orai1/Orai3 channel through phosphorylation of STIM1 in HEK-293 cells (43).…”

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

“…9). Similarly, adenosine in rat cerebral and coronary artery SMCs (1169), arginine vasopressin in rat retinal arteriolar SMCs (691) and pituitary adenylate cyclase activating polypeptide in rat cerebral artery SMCs (776) act via the cAMP-PKA signaling cascade to stimulate Ca 2+ spark frequency (Fig. 9).…”