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Ganesh Prasanna, Adnan I. Dibas, Thomas Yorio; Cholinergic and Adrenergic Modulation of the Ca2+ Response to Endothelin-1 in Human Ciliary Muscle Cells. Invest. Ophthalmol. Vis. Sci. 2000;41(5):1142-1148.
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purpose. To determine the cholinergic (carbachol, CCH) and adrenergic
(norepinephrine, NE) modulation of Ca2+ response to
endothelin-1 in human ciliary smooth muscle (HCSM) cells.
methods. Intracellular calcium levels were measured using the Fura-2 calcium
imaging system in HCSM cells treated either singly with endothelin-1
(ET-1; 2–200 nM), CCH (1–100 μM), NE (0.1–10 μM) or
isoproterenol (ISO; 1 μM) or in combinations of CCH, NE, or ISO with
ET-1. Intracellular cAMP levels after NE and ISO treatments were also
measured using a radioimmunoassay.
results. Endothelin-1 dose-dependently increased[
Ca2+]i and was characteristically biphasic
(peak [Ca2+]i for ET-1: 2 nM, 517 ± 73
nM; 20 nM, 785 ± 65 nM; and 200 nM, 2564 ± 359 nM).
Carbachol also dose-dependently increased[
Ca2+]i; however, subsequent additions of
ET-1 (200 nM) resulted in lower [Ca2+]i (100μ
M CCH + ET-1; 300 ± 21 nM) compared with that observed with
200 nM ET-1 alone (2564 ± 359 nM). Norepinephrine pretreatment
also decreased ET-1–induced [Ca2+]i (10 μM
NE + ET-1; 619 ± 64 nM) compared with ET-1 alone, and NE’s
effect could be reversed by propranolol (β-adrenergic antagonist)
treatment. Neither CCH nor NE was able to completely abolish ET-1’s
ability to mobilize calcium in HCSM cells. Isoproterenol (aβ
-agonist) mimicked NE’s effect on ET-1–induced[
Ca2+]i (1 μM ISO + ET-1; 254 ± 56
nM). Both ISO and NE elevated [cAMP] in HCSM cells.
conclusions. In HCSM cells, CCH and ET-1 can activate common as well as specific[
Ca2+]i pools. The reduction in ET-1–induced[
Ca2+]i after NE/ISO treatment appears to be
due to elevated cAMP levels via β-receptor activation, suggesting the
existence of receptor cross talk. The ability of CCH and NE to modulate
ET-1’s actions on HCSM may be relevant to the regulation of ciliary
muscle contraction and aqueous humor outflow.
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