Pneumadin-evoked intracellular free Ca2+ responses in rat aortic smooth muscle cells: effect of dexamethasone.
The direct vascular effect of pneumadin (PN) was determined by studying the changes in intracellular free calcium ([Ca2+]i) levels in cultured rat aortic smooth muscle cells maintained between the second and fifth passages. PN evoked a rapid, concentration-dependent, biphasic increase in [Ca2+]i. The [Ca2+]i level rose from a basal value of 108 nM to a maximum increase in peak value of 170 nM. Although the level of maximal [Ca2+]i response evoked by PN was less than with other vasoactive agonists, it was more potent (EC50 0.5 nM) than even endothelin-1 (EC50 3.1 nM). At concentrations > 100 nM, [Ca2+]i elevations induced by PN above basal levels were no longer observed. Pretreatment with dexamethasone (100 nM for 24 hr) resulted in a significant increase (P < 0.01) in the peak [Ca2+]i response (310 nM) to PN. However, the biphasic pattern in the peak [Ca2+]i responses encountered with increasing concentrations of PN remained unaffected. The exaggerated [Ca2+]i response to PN was abolished by preincubation of cells with either the glucocorticoid antagonist mifepristone (RU 486) or the protein synthesis inhibitor cycloheximide. Inclusion of either an AT1 antagonist (losartan), a V1 selective vasopressin antagonist (d(Ch2)5 Tyr (Me) AVP), or an alpha-adrenoceptor antagonist (phentolamine) failed to affect the increases in [Ca2+]i induced by PN. PN-evoked increases in inositol 1,4,5-trisphosphate levels paralleled the [Ca2+]i changes. These data suggest that PN increases Ca2+ mobilization in rat aortic smooth muscle cells via activation of phospholipase C coupled receptors. This effect is up-regulated by dexamethasone.
Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
V K
VK
Batra
R L
RL
Hopfner
V
V
Gopalakrishnan
J R
JR
McNeill
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D001011:Aorta; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D004347:Drug Interactions; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000378:metabolism; D014667:Vasopressins / Q000494:pharmacology*
D000893:Anti-Inflammatory Agents; D009842:Oligopeptides; D011956:Receptors, Cell Surface; D014667:Vasopressins; C066922:pneumadin; D003907:Dexamethasone; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium