cAMP/PKA-dependent increases in Ca Sparks, oscillations and SR Ca stores in retinal arteriolar myocytes after exposure to vasopressin.
OBJECTIVE
To investigate the effects of arginine vasopressin (AVP) on Ca(2+) sparks and oscillations and on sarcoplasmic reticulum (SR) Ca(2+) 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(2+) store content was assessed by recording caffeine-induced Ca(2+) transients with microfluorimetry and fura-2.


RESULTS
The frequencies of Ca(2+) 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(2+) 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(2+)](i).


CONCLUSIONS
AVP activates a cAMP/PKA-dependent pathway via V(1a) receptors in retinal arteriolar smooth muscle. This effect persistently increases SR Ca(2+) loading, upregulating Ca(2+) sparks and oscillations, and may favor prolonged agonist activity despite receptor desensitization.
Jeffries
Owen
O
Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Sciences, The Royal Victoria Hospital, Belfast, Northern Ireland, United Kingdom.
McGahon
Mary K
MK
Bankhead
Peter
P
Lozano
Maria Manfredi
MM
Scholfield
C Norman
CN
Curtis
Tim M
TM
McGeown
J Graham
JG
D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D065092:Antidiuretic Hormone Receptor Antagonists; D001127:Arginine Vasopressin / Q000494:pharmacology*; D001160:Arterioles / Q000187:drug effects / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005470:Fluorometry; D016257:Fura-2 / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D018613:Microscopy, Confocal; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D011759:Pyrrolidines / Q000494:pharmacology; D017483:Receptors, Vasopressin / Q000378:metabolism; D012161:Retinal Artery / Q000187:drug effects / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013552:Swine; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014966:Xanthenes / Q000378:metabolism
D000814:Aniline Compounds; D065092:Antidiuretic Hormone Receptor Antagonists; C409648:Fluo 4; D007211:Indoles; D011759:Pyrrolidines; D017483:Receptors, Vasopressin; D014662:Vasoconstrictor Agents; D014966:Xanthenes; D001127:Arginine Vasopressin; D002110:Caffeine; C082134:relcovaptan; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium; D016257:Fura-2