Calcium dependence of the stimulatory action of hypertonicity on renal medullary prostaglandin synthesis.
Previous studies have shown that hypertonic mannitol or NaCl increases the release of [3H]arachidonate and immunoreactive prostaglandin E in inner medullary slices incubated in Ca2+-free media containing EGTA. By contrast, the stimulation of these parameters by ionophore A23187 and by arginine-vasopressin are abolished in Ca2+-free media plus EGTA. In the present study, the effects of Ca2+ deprivation and the intracellular Ca2+ antagonist TMB-8 [8-N,N-diethylamino)octyl-3,4,5 -trimethoxybenzoate-HCl) were further examined to assess the Ca2+ dependence of the actions of different stimuli of prostaglandin E synthesis in rat renal inner medulla. Ca2+-free media without EGTA abolished increases in [3H]arachidonate and immunoreactive prostaglandin E release induced by ionophore A23187, but not those induced by arginine-vasopressin, suggesting that different pools of Ca2+ subserve expression of the actions of these two stimuli. At low concentrations, TMB-8 (10-25 microM) inhibited increases in [3H]arachidonate and immunoreactive prostaglandin E release induced by arginine-vasopressin, but did not influence effects of Ca2+ plus ionophore A23187 or hypertonicity on these parameters. At higher concentrations (100-500 microM), TMB-8 suppressed effects of ionophore A23187, hyperosmolar NaCl and mannitol on immunoreactive prostaglandin E and [3H]arachidonate release from slices. The effects of a sub-optimal inhibitory concentration of TMB-8 on ionophore A23187 actions were overcome by increasing Ca2+ in the media from 1.5 to 5 mM. Ca2+ deprivation, or concentrations of EGTA or TMB-8, that were effective in suppressing increases in immunoreactive prostaglandin E induced by ionophore A23187, arginine-vasopressin or hypertonicity, did not modify increases in immunoreactive prostaglandin E induced by exogenous arachidonate. Moreover, in microsomal fractions of inner medulla, TMB-8 suppressed Ca2+-dependent increases in phospholipase A2 and C activities, an effect which was competitive with Ca2+. Thus, Ca2+ deprivation and TMB-8 act at a step in the immunoreactive prostaglandin E synthetic pathway proximal to cyclooxygenase activity, and probably at the level of Ca2+-dependent acyl hydrolase activity. The results with TMB-8 indicate that an intracellular pool of Ca2+ is involved in expression of the actions of hypertonicity to increase [3H]arachidonate release and immunoreactive prostaglandin E in inner medulla.
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D001127:Arginine Vasopressin / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D005260:Female; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007679:Kidney Medulla / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D011453:Prostaglandins / Q000096:biosynthesis*; D011458:Prostaglandins E / Q000096:biosynthesis; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D014882:Water-Electrolyte Balance
D001095:Arachidonic Acids; D011453:Prostaglandins; D011458:Prostaglandins E; D001127:Arginine Vasopressin; D016718:Arachidonic Acid; D000001:Calcimycin; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D011494:Protein Kinases; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium