Renal function of isolated perfused kidneys from hypertensive (MHS) and normotensive (MNS) rats of the Milan strain: role of calcium.
Abnormal sodium (Na+) and water handling by the kidney may be the cause of hypertension in rats of the Milan hypertensive strain (MHS). In addition, the plasma cell membrane Ca-ATPase at Vmax is lower in MHS than in normotensive controls (MNS). The isolated kidney preparation was used to explore the role of extracellular free calcium (Ca2+) concentrations (1.25, 1.00 and 0.75 mmol/l) in tubular Na+ transport of pre-hypertensive MHS rats. At the Ca2+ concentration of 1.0 mmol/l, the following parameters were significantly higher (P less than 0.01) in MHS: glomerular filtration rate (GFR) and urinary volume (UV), +104.8 and +147.2%, respectively; urinary Na+ excretion (UNa+), +318.0%; tubular Na+ reabsorption (TNa+), +91.0% and oxygen consumption Q O2, +42.9%. Raising the Ca2+ concentration to 1.25 mmol/l increased UV (+167.0%) and UNa+ (+231.0%) in MHS without substantially affecting MNS. The difference between the two strains was therefore considerably larger for these parameters, but disappeared for TNa+ and Q O2. The overall kidney function of MHS was poor as compared wit renal function at Ca2+ 1.0 mmol/l. The differences between the two strains virtually disappeared at the lowest Ca2+ concentration (0.75 mmol/l); only GFR and TNa+ remained slightly greater in MHS mainly because of the poor viability of MNS kidneys in this experimental condition. It thus appears that the lower activity of Ca2+-ATPase of MHS compared with MNS plasma cell membranes influences the differences in Na+ and water handling in the two strains.
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D006973:Hypertension / Q000503:physiopathology* / Q000652:urine; D007668:Kidney / Q000502:physiology / Q000503:physiopathology*; D007671:Kidney Concentrating Ability; D007684:Kidney Tubules / Q000378:metabolism; D010477:Perfusion; D011312:Pressure; D051381:Rats; D012964:Sodium / Q000378:metabolism / Q000652:urine
D012964:Sodium; D002118:Calcium