Effects of endothelin on phospholipases and generation of second messengers in cat iris sphincter and SV-CISM-2 cells.
In both immortalized cat iris sphincter smooth muscle cells (SV-CISM-2 cells) and cat iris sphincter, endothelin-1 (ET-1) markedly increased the activities of phospholipase A2 (PLA2), as measured by the release of arachidonic acid (AA), phospholipase C (PLC), as measured by the production of inositol trisphosphate (IP3), and phospholipase D (PLD), as measured by the formation of phosphatidylethanol (PEt). In SV-CISM-2 cells, ET-1 induced AA release, IP3 production and PEt formation in a dose- and time-dependent manner. The dose-response studies showed that the peptide is more potent in activating PLD (EC50 = 1.2 nM) than in activating PLC (EC50 = 1.5 nM) or PLA2 (EC50 = 1.7 nM). The time course studies revealed that ET-1 activated the phospholipases in a temporal sequence in which PLA2 was stimulated first (t1/2 = 12 s), followed by PLC (t1/2 = 48 s) and lastly PLD (t1/2 = 106 s). In SV-CISM-2 cells, in contrast to the intact iris sphincter, sarafotoxin-c, an ETB receptor agonist, had no effect on the phospholipases, and indomethacin, a cyclooxygenase inhibitor, had no effect on the stimulatory effect of ET-1 on the phospholipases. These results suggest that in this smooth muscle cell line, ET-1 interacts with the ETA receptor subtype to activate, via G proteins, phospholipases A2, C and D in a temporal sequence.
Abdel-Latif
A A
AA
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912, USA.
Ding
K H
KH
Akhtar
R A
RA
Yousufzai
S Y
SY
D000818:Animals; D002415:Cats; D002460:Cell Line; D019332:Endothelin-1 / Q000494:pharmacology*; D007498:Iris / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism*; D010740:Phospholipases / Q000187:drug effects*; D015290:Second Messenger Systems / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects*
D019332:Endothelin-1; D010740:Phospholipases