Our results demonstrate that (1) [Ca(2+)](i), intracellular calcium stores and the capacitative calcium entry were significantly increased already in early stages of CKD; (2) long-term vitamin D(3) supplementation normalized [Ca(2+)](i) without any effect on intracellular calcium reserves or the capacitative calcium entry.

Pseudouridine (ψ) is an outstanding nucleoside which is not rebuilt into the tRNA once the parent tRNA is broken down, ψ inhibits basal glucose utilization in isolated rat soleus muscle with intact membrane with AD₅₀ 42 μmol/l and C_max 66%. ψ at concentrations found in renal failure patients inhibits both the insulin-and tolbutamide-stimulated glucose utilization. Its inhibitory activity is partially additive with diltiazem inhibition and nonadditive in the case of magnesium depletion. It is concluded that ψ inhibits glucose utilization at the level of Ca modulation in the insulin regulatory cascade.

Background: Data on the efficacy and safety of long-term vitamin D supplementation in chronic kidney disease (CKD) are scarce. We assessed the effects of the 12-month vitamin D₃ treatment on mineral metabolism and calciotropic hormones in patients with CKD stages 2–4. Methods: Eighty-seven patients (mean age 66 years, men/women 33/54) were randomized to cholecalciferol treatment with either 5,000 or 20,000 IU/week. Serum calcium, phosphate, 25(OH)D₃, 1,25(OH)₂D₃, PTH and urinary mineral concentrations were obtained at baseline and after 4, 8 and 12 months. Results: The median serum mineral concentrations were normal and not changed throughout the study. The number of hypercalciuric patients slightly increased with higher dose, but no sustained rise in calciuria was present. Vitamin D insufficiency/deficiency was revealed in 72 (83%) patients at baseline and 37 (43%) at month 12. The 25(OH)D₃ levels increased more with higher dose; a rise in 1,25(OH)₂D₃ was less impressive. The parathyroid hormone (PTH) concentrations were reduced, but the number of subjects with PTH below the lower limit for CKD stage 3 increased equally with both doses. Conclusions: Vitamin D insufficiency/deficiency in CKD significantly improved after the 12-month cholecalciferol treatment, with higher dose being more effective and equally safe. Further studies of vitamin D₃ effects on bone metabolism are warranted.

Pseudouridine (Ψ) is a unique nucleoside accumulated in the sera of renal failure (RF) patients. Surprisingly data on its excretion are lacking. To get an overview, the Ψ serum level and urinary excretion were investigated in 73 healthy subjects (C), 16 patients not on dialysis (ND) and 12 hemodialysis patients (D). It was found: (a) Ψ accumulates in the sera of both ND and D patients. An inverse power correlation fits best with the relationship between serum Ψ and the clearance of endogenous creatinine (C_Cr)· The amount of Ψ filtered in glomeruli of ND patients increases while it remains practically unchanged in D patients. However, the Ψ filtration load of residual nephrons increases with the decreasing C_Cr as a consequence of its increased serum concentration, (b) Both Ψ net resorption and secretion have been found in C subjects. The increased Ψ resorption diminishes the necessary increase of Ψ urinary excretion both in ND and D patients. The increase of Ψ resorption is marked if calculated on residual nephrons. (c) The slightly decreased Ψ excretion excludes the participation of its increased synthesis in its accumulation in RF. It is concluded that Ψ accumulation in RF is caused by the impairment of its kidney excretion and the increased Ψ resorption participates markedly in its retention.

We investigated whether 4-aminopyridine (4AP), a drug recently linked to calcium influx and apoptosis, also affected purinergic receptor channels that are known to play an important role in the activation of T lymphocytes. The application of 4AP induced a rise in [Ca2+]i that was sensitive to nickel. This action was also observed in cells in which calcium reserves were emptied using thapsigargin (Tg). However, it was not present in the absence of extracellular Ca2+, despite full internal reserves. Adenosine trisphosphate (ATP), a partial agonist and a physiological activator of purinergic receptors, also stimulated Ca2+ entry independently of the calcium release from internal compartments. The effects of 4AP and ATP were not additive when studied on the same population of cells. KN-62 inhibited an increase in calcium entry induced by 4AP, while brilliant blue G (BBG) prevented it, supporting the hypothesis that purinergic P2X7 receptors are involved in this action. Furthermore, 4AP allowed entry of ethidium bromide (314 Da) but not propidium iodide (415 Da) into the cell, also corroborating the involvement of P2X7 pores. The presented results demonstrate, for the first time in human mononuclear cells isolated from healthy volunteers, that the P2X7 channel pore is involved in the action of 4AP and intervenes in the sustained calcium entry induced in response to 4AP.