Inhibitory effect of high [Mg2+] on the vasopressin-stimulated hydroosmotic permeability of the isolated perfused cortical collecting duct

High magnesium concentration inhibits the effect of arginine vasopressin (A VP) on smooth muscle contraction and platelet aggregation and also influenc es hepatocyte AVP receptor binding. The aim of this study was to determine the role of magnesium concentration [Mg2+] in AVP-stimulated water transpor t in the kidney collecting duct. The effect of low and high peritubular [Mg 2+] on the AVP-stimulated osmotic water permeability coefficient (P-f) was evaluated in the isolated perfused rabbit cortical collecting duct (CCD). C ontrol tubules bathed and perfused with standard Ringer bicarbonate solutio n containing 1 mM Mg2+ presented a P-f of 223.9 +/- 27.2 mu m/s. When Mg2was not added to the bathing solution, an increase in the AVP-stimulated P- f to 363.1 +/- 57.2 mu m/s (P<0.05) was observed. An elevation of Mg2+ to 5 mM resulted in a decrease in P-f to 202.9 +/- 12.6 mu m/ s (P<0.05). This decrease in the AVP-stimulated Pf at 5 mM Mg2+ persisted when the CCDs were returned to 1 mM Mg2+, P-f = 130.2 +/- 20.3 mu m/s, and was not normalized by the addition of 8-[4-chlorophenylthio]-adenosine 3',5'-cyclic monophosp hate, a cAMP analogue, to the preparation. These data indicate that magnesi um may play a modulatory role in the action of AVP on CCD osmotic water per meability, as observed in other tissues.