Synergistic effect of adrenergic and muscarinic receptor activation on [Ca2+]i in rabbit ciliary body epithelium.
1. Changes in cytosolic free calcium concentration ([Ca2+]i) in response to cholinergic and adrenergic agents alone and in combination were investigated using fura-2 fluorescence imaging in intact non-pigmented epithelial cells of rabbit ciliary body. 2. Resting ('baseline') [Ca2+]i was 147 +/- 6 nM (mean +/- S.E.M.). Acetylcholine (ACh, 10 microM) doubled [Ca2+]i, and adrenaline (1 microM) increased it by about 36%. When ACh (10 microM) and adrenaline (1 microM) were applied together [Ca2+]i was transiently increased to 1160 +/- 160 nM, about 7 times the response induced by ACh alone. 3. Noradrenaline and 5-bromo-6-(2-imidazolin-2-yl-amino)-quinoxaline (UK 14304) had effects similar to adrenaline in enhancing the response to ACh. Phenylephrine (Phe) had a relatively smaller effect and none was observed for methoxamine and isoprenaline (Iso). 4. The response to ACh and adrenaline could be blocked by atropine (1 microM, 87 +/- 5%), yohimbine (1 microM, 73 +/- 8%), and to a lesser degree by prazosin (1 microM). Propranolol had no effect. 5. Lowering the extracellular calcium concentration to 3 nM dropped the baseline [Ca2+]i by half and reduced the response to ACh and adrenaline to a small and transient rise in [Ca2+]i. Addition of La3+ to Ca(2+)-containing solution also lowered [Ca2+]i and largely reduced the response. 6. We conclude that simultaneous activation of muscarinic and alpha 2-adrenergic receptors induces a large increase in [Ca2+]i, which is the result of both Ca2+ release and influx.
Farahbakhsh
N A
NA
Jules Stein Eye Institute, UCLA School of Medicine 90024-7008.
Cilluffo
M C
MC
D000109:Acetylcholine / Q000494:pharmacology; D000322:Adrenergic Agonists / Q000494:pharmacology; D018674:Adrenergic Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D002924:Ciliary Body / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D007811:Lanthanum / Q000378:metabolism; D008856:Microscopy, Fluorescence; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*
D000322:Adrenergic Agonists; D018674:Adrenergic Antagonists; D011942:Receptors, Adrenergic, alpha; D011976:Receptors, Muscarinic; D007811:Lanthanum; D000109:Acetylcholine; D002118:Calcium; D004837:Epinephrine