Calcium and prostaglandin E2 in renomedullary interstitial cells

Renomedullary interstitial cells cultured from the Dahl salt-resistant rat have higher levels of basal cytosolic calcium and prostaglandin E2 and are more responsive to vasopressin than interstitial cells from the Dahl salt-sensitive rat. We examined the potential role of inositol phospholipid hydrolysis in mediating these differences. Vasopressin-induced increases in labeled inositol phosphates were enhanced in renomedullary interstitial cells from Dahl salt-resistant compared with those from salt-sensitive rats. Addition of neomycin reduced basal production of labeled inositol phosphates and abolished the increase in inositol phosphates induced by vasopressin. Neomycin also prevented the peak decline pattern in cytosolic Ca2+ seen with vasopressin but did not influence basal cytosolic Ca2+. In the presence of neomycin, vasopressin induced a modest but prolonged increase in cytosolic calcium. In contrast to its marked effects on inositol phosphate production, neomycin was without effect on basal or vasopressin-responsive prostaglandin E2 production. Moreover, basal and vasopressin-induced increases in cytosolic Ca2+ remained higher in renomedullary interstitial cells from Dahl salt-resistant versus those from salt-sensitive rats exposed to neomycin. The results do not support a requirement for phospholipase C-induced inositol phospholipid hydrolysis in the mediation of vasopressin actions on prostaglandin E2 production by renomedullary interstitial cells and imply that the differences in cytosolic Ca2+ and prostaglandin E2 seen in these two cell lines are not related to differences in inositol phospholipid metabolism.