Cholinergic and adrenergic modulation of the Ca2+ response to endothelin-1in human ciliary muscle cells

PURPOSE. To determine the cholinergic (carbachol. CCH) and adrenergic (nore pinephrine, NE) modulation of Ca2+ response to endothelin-1 in human ciliar y smooth muscle (HCSM) cells. METHODS. Intracellular calcium levels were measured using the Fura-2 calciu m imaging system in HCSM cells treated either singly with endothelin-1 (ET- 1; 2-200 nM), CCH (1-100 mu M), NE (0.1-10 mu M) or isoproterenol (ISO; 1 m u M) or in combinations of CCH, NE, or ISO with ET-1. Intracellular cAMP le vels after NE and ISO treatments were also measured using a radioimmunoassa y. RESULTS. Endothelin-1 dose-dependently increased [Ca2+](i) and was characte ristically biphasic (peak [Ca2+](i) for ET-1: 2 nM, 517 +/- 73 nM; 20 nM, 7 85 +/- 65 nM; and 200 nM, 2564 +/- 359 nM). Carbachol also dose-dependently increased [Ca2+](i); however, subsequent additions of ET-1 (200 nM) result ed in lower [Ca2+](i) (100 mu M CCH + ET-1, 300 +/- 21 nM) compared with th at observed with 200 nM ET-1 alone (2564 +/- 359 nM). Norepinephrine pretre atment also decreased ET-1-induccd [Ca2+](i) (10 mu M NE + ET-1, 619 +/- 64 nM) compared with ET-1 alone, and NE's effect could be reversed by propran oiol (beta-adrenergic antagonist) treatment. Neither CCH nor NE was able to completely abolish ET-1's ability to mobilize calcium in HCSM cells. Isopr oterenol (a beta-agonist) mimicked NE's effect on ET-1-induced [Ca2+](i) (1 mu M ISO + ET-1; 254 +/- 56 nM). Both ISO and NE elevated [cAMP] in HCSM c ells. CONCLUSIONS. In HCSM cells, CCH and ET-1 can activate common as well Is spe cific [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 acti vation, 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 regulatio n of ciliary muscle contraction and aqueous humor outflow.