Caveolae-dependent internalization and homologous desensitization of VIP/PACAP receptor, VPAC₂, in gastrointestinal smooth muscle

The main membrane proteins of caveolae (caveolin-1, -2 and -3) oligomerize within lipid rich domains to form regular invaginations of smooth muscle plasma membrane and participate in receptor internalization and desensitization independent of clathrin-coated vesicle endocytosis. We have previously shown that Gs-coupled VIP/PACAP receptors, VPAC2, predominantly expressed in smooth muscle cells of the gut, are exclusively phosphorylated by GRK2 leading to receptor internalization and desensitization. Herein, we characterized the role of caveolin-1 in VPAC2 receptor internalization and desensitization in gastric smooth muscle using three approaches: (i) methyl β-cyclodextrin (MβCD) to deplete cholesterol and disrupt caveolae in dispersed muscle cells, (ii) caveolin-1 siRNA to suppress caveolin-1 expression in cultured muscle cells, and (iii) caveolin-1 knockout mice (caveolin-1(-/-)). Pretreatment of gastric muscle cells with VIP stimulated tyrosine phosphorylation of caveolin-1, and induced VPAC2 receptor internalization (measured as decrease in (125)I-VIP binding after pretreatment) and desensitization (measured as decrease in VIP-induced cAMP formation after pretreatment). Caveolin-1 phosphorylation, and VPAC2 receptor internalization and desensitization were blocked by disruption of caveolae with MβCD, suppression of caveolin-1 with caveolin-1 siRNA or inhibition of Src kinase activity by PP2. Pretreatment with VIP significantly inhibited adenylyl cyclase activity and muscle relaxation in response to subsequent addition of VIP in freshly dispersed muscle cells and in muscle strips isolated from wild type and caveolin-1(-/-) mice; however, the inhibition was significantly attenuated in caveolin-1(-/-) mice. These results suggest that caveolin-1 plays an important role in VPAC2 receptor internalization and desensitization.

Long-term follow-up of the remaining kidney in living related kidney donors

In this work 45 living related kidney donors (LRD) and 20 healthy sex and age matched controls were examined. Donors were evaluated up to 122 months after donation. Hyperfiltration was observed in the remaining kidney with a mean one-kidney GFR value of 82.9 +/- 36.8 ml/min while the control value was 71.04 +/- 31.5 ml/min. The kidney was significantly larger in the donor group than in the controls. In the LRD group, 3 were hypertensive, 7 showed microscopic haematuria and 5 had mild proteinuria. In the control group 3 were mildly hypertensive, and 2 showed microscopic haematuria. Serum creatinine of the donor group was found to be significantly higher than in the controls, yet it was stable and within the normal range (0.89 +/- 0.28 mg/dl). Examination for microalbuminuria showed that 11% of the donor group excreted higher amounts of albumin, being above the upper limit of the control group. We have concluded that kidney donation will result in minor abnormalities in kidney functions which will not affect the donor morbidity or mortality.

Determination of red-cell mass in assessment and management of anaemia in babies needing blood transfusion

A new method for the rapid determination of red-blood-cell mass (RCM) in infants needing blood transfusion is described. RCM is estimated from the fall in the baby's fetal haemoglobin level resulting from transfusion of a known mass of adult-haemoglobin-containing red cells. In severe blood loss and refractory anaemias in preterm infants, in addition to the red-cell deficit, the plasma volume is low, leading to a falsely high haematocrit of about 0.30, which conceals a deficiency of 50-70% in circulating red cells. Red-cell transfusion in such infants based on haematocrit often fails to restore RCM to normal, leading to repeated transfusions. The frequency of transfusions may be reduced by giving enough red cells fully to correct the deficiency based on RCM estimation.