Cholinergic and adrenergic modulation of the Ca2+ response to endothelin-1 in human ciliary muscle cells.
OBJECTIVE
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 microM), NE (0.1-10 microM) or isoproterenol (ISO; 1 microM) 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 (100 microM 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 microM NE + ET-1; 619 +/- 64 nM) compared with ET-1 alone, and NE's effect could be reversed by propranolol (beta-adrenergic antagonist) treatment. Neither CCH nor NE was able to completely abolish ET-1's ability to mobilize calcium in HCSM cells. Isoproterenol (a beta-agonist) mimicked NE's effect on ET-1-induced [Ca2+]i (1 microM 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 beta-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.
Prasanna
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Department of Pharmacology, University of North Texas Health Science Center, Fort Worth 76107, USA. gprasann@molly.hsc.unt.edu
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D000322:Adrenergic Agonists / Q000494:pharmacology*; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol; D002460:Cell Line; D018679:Cholinergic Agonists / Q000494:pharmacology*; D002924:Ciliary Body / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D019332:Endothelin-1 / Q000494:pharmacology*; D004963:Estrenes / Q000494:pharmacology; D016257:Fura-2 / Q000378:metabolism; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine; D011760:Pyrrolidinones / Q000494:pharmacology; D011863:Radioimmunoassay; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D000322:Adrenergic Agonists; D018679:Cholinergic Agonists; D004338:Drug Combinations; D019332:Endothelin-1; D004963:Estrenes; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D003994:Bucladesine; D002217:Carbachol; D000242:Cyclic AMP; D010738:Type C Phospholipases; D007545:Isoproterenol; D002118:Calcium; D016257:Fura-2; D009638:Norepinephrine