Calcium and O2-dependent control of inner medullary cGMP: possible role for Ca2+-dependent arachiodonate release and prostaglandin synthesis in expression of the action of osmolality on renal inner medullary guanosine 3'5' monophosphate.
The present study examined the effects of osmolality on basal cGMP metabolism and cGMP responses to carbamylcholine in rat inner medulla. The basal cGMP content of inner medullary slices and cGMP responses to carbamylcholine fell as media osmolality was increased from 305 to 1650 mosmole/liter by the addition of urea plus NaCl to standard Krebs bicarbonate buffer. Exclusion of extracellular Ca2+ or addition of tetracaine abolished the effects of both a reduction in osmolality and carbamylcholine to increase cGMP. Readdition of Ca2+ to Ca2+-deprived slices restored the actions of media osmolality and carbamylcholine on cGMP. Ionophore A23187 enhanced the effects of Ca2+ to increase slice cGMP content. Analogous to the effects of Ca2+ alone, increases in cGMP accumulation in response to Ca2+ plus A23187 were significantly suppressed at high osmolality. In slices prelabeled with [14C]-arachidonate, the stimulatory effects of Ca2+ plus A23187 on cGMP were correlated with enhanced release of [14C]-arachidonate into the media and with increased accumulation of prostaglandin E in the media, all of which were depressed in slices incubated at 1650 compared to 750 mosmole/liter. Exogenous arachidonate increased cGMP 50% to twofold in the absence of Ca2+. However, the effects of exogenous arachidonate on cGMP were clearly less than those of either Ca2+ or carbamylcholine. Addition of indomethacin or exclusion of O2 abolished effects of exogenous arachidonate, Ca2+ plus A23187, reduced osmolality, and carbamylcholine to increase cGMP. In the presence of indomethacin or in the absence of O2, Ca2+, and arachidonate-induced prostaglandin E accumulation was also not detectable. By contrast, addition of indomethacin or exclusion of O2 had no effect on Ca2+-induced [14C]-arachidonate release. Changes in cGMP accumulation in inner medulla in response to changes in media osmolality, Ca2+ plus A23187, and exogenous arachidonate were accompanied by directionally similar alterations in cAMP. Moreover, increases in cAMP induced by Ca2+ or arachidonate were inhibited by indomethacin and O2 deprivation. These data suggest that Ca2+-dependent fatty acid release and oxygenation by fatty acid release and oxygenation by cyclooxygenase may participate in the control of the metabolism of both cGMP and cAMP in inner medulla. However, PGE2 and PGI2 increased cAMP but not cGMP, whereas carbamylcholine increased cGMP but not cAMP. Thus, to the extent that arachidonate oxygenation products mediate changes in cyclic nucleotide metabolism in inner medulla, it is likely that more than one product is involved or that changes in cGMP and cAMP occur in separate compartments of inner medulla.
D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002217:Carbachol / Q000494:pharmacology; D006152:Cyclic GMP / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism*; D009994:Osmolar Concentration; D010100:Oxygen / Q000494:pharmacology*; D011458:Prostaglandins E / Q000378:metabolism; D051381:Rats
D001095:Arachidonic Acids; D011458:Prostaglandins E; D000001:Calcimycin; D002217:Carbachol; D006152:Cyclic GMP; D010100:Oxygen; D002118:Calcium; D007213:Indomethacin