Arginine]vasopressin hydrolyses phosphoinositides in the medullary thick ascending limb of mouse nephron

Abstract

NaCl reabsorption across the thick ascending limb of Henle's loop (TAL) is stimulated by several hormones, in particular vasopressin acting through V2 receptors and cyclic AMP production. This study used suspensions of medullary TAL (mTAL) tubules from the mouse nephron to investigate the possibility that, besides activating adenylyl cyclase, vasopressin also stimulates phospholipase C via V1 receptor occupancy. Two different methods, phosphoinositide labelling and inositol trisphosphate (InsP3) radioimmunoassay, were used to show that [arginine]vasopressin (AVP) rapidly stimulated the formation of InsP3, which peaked at 200%-250% of control within the first minute of incubation with 10 nmol/l vasopressin at 37 degrees C, and declined to basal level after 5-10 min. Dose/response curves for InsP3, established at 30 degrees C and 37 degrees C using radioimmunoassay, showed a half-maximal stimulation of InsP3 production at about 1 nmol/l AVP and a maximal response at 10 nmol/l. Similar values were obtained for the response to AVP in terms of cAMP accumulation. InsP3 content in the presence of higher concentrations of AVP (1 mumol/l) was significantly lower (P < 0.001) than in the presence of 10 nmol/l AVP, giving a bell-shaped appearance to the dose/response curve at 37 degrees C but not at 30 degrees C. The V2 receptor agonist, 1-deamino-[8-D-Arg]vasopressin (dAVP) did not stimulate the formation of InsP3, and the V1 receptor antagonist d(CH2)5[Tyr(Me)2]AVP inhibited AVP-induced InsP3 formation, which therefore appeared to be mediated by V1 receptor occupancy. Under the same conditions, AVP also induced the formation of diradylglycerol via V1 receptor activation, with an analogous dose/response curve.(ABSTRACT TRUNCATED AT 250 WORDS)