Action of ANP on the nongenomic dose-dependent biphasic effect of aldosterone on NHE1 in proximal S3 segment.

The rapid (2 min) nongenomic effects of aldosterone (ALDO) and/or spironolactone (MR antagonist), RU 486 (GR antagonist), atrial natriuretic peptide (ANP) and dimethyl-BAPTA (BAPTA) on the intracellular pH recovery rate (pHirr) via NHE1 (basolateral Na⁺/H⁺ exchanger isoform), after the acid load induced by NH4Cl, and on the cytosolic free calcium concentration ([Ca²âº](i)) were investigated in the proximal S3 segment isolated from rats, by the probes BCECF-AM and FLUO-4-AM, respectively. The basal pHi was 7.15±0.008 and the basal pHirr was 0.195±0.012 pH units/min (number of tubules/number of tubular areas=16/96). Our results confirmed the rapid biphasic effect of ALDO on NHE1: ALDO (10⁻¹² M) increases the pHirr to approximately 59% of control value, and ALDO (10⁻6 M) decreases it to approximately 49%. Spironolactone did not change these effects, but RU 486 inhibited the stimulatory effect and maintained the inhibitory effect. ANP (10⁻6 M) or BAPTA (5×10⁻5 M) alone had no significant effect on NHE1 but prevented both effects of ALDO on this exchanger. The basal [Ca²âº](i) was 104±3 nM (15), and ALDO (10⁻¹² or 10⁻6 M) increased the basal [Ca²âº](i) to approximately 50% or 124%, respectively. RU 486, ANP and BAPTA decreased the [Ca²âº](i) and inhibited the stimulatory effect of both doses of ALDO. The results suggest the involvement of GR on the nongenomic effects of ALDO and indicate a pHirr-regulating role for [Ca²âº](i) that is mediated by NHE1, stimulated/impaired by ALDO, and affected by ANP or BAPTA with ALDO. The observed nongenomic hormonal interaction in the S3 segment may represent a rapid and physiologically relevant regulatory mechanism in the intact animal under conditions of volume alterations.

Effects of NH4Cl intake on renal growth in rats: role of MAPK signalling pathway.

BACKGROUND: There is a surprising lack of experimental data on the mechanisms of NH4Cl-induced chronic metabolic acidosis which causes kidney hypertrophy. The NH4Cl treatment results in an absolute increase in kidney mass. Despite findings to indicate a close interaction between NH4Cl-induced chronic metabolic acidosis and renal enlargement, the role of the stimulated serine kinase cascade, mediated by the stepwise activation of extracellular signal-regulated kinase (ERK) signalling, on kidney hypertrophy has not yet been investigated. METHODS: To test this hypothesis, the present study was undertaken to further explore the possible involvement of mitogen-activated protein kinase (MAPK) signalling pathway in renal growth in chronic NH4Cl-treated rats by western blot analysis. RESULTS: Our major findings are as follows: (1) Urinary sodium excretion significantly increased during the early phases of NH4Cl-induced acidosis, (2) This occurrence is associated with sustained renal hypertrophy, and (3) sustained basal phosphorylation of IRS-1, Shc, and MAPK/ERKs in acidotic kidneys. CONCLUSIONS: The present study confirms that NH4Cl-induced acidosis causes disturbances in renal sodium handling. In addition, these findings demonstrate a sustained pre-stimuli activation of kidney MAPK/ERKs signalling pathways in the NH4Cl-treated rats that may correlate with an increased rate of kidney hypertrophy and a transient renal tubule inability to handle sodium. Thus, the altered renal electrolyte handling may result from a reciprocal relationship between the level of renal tubule metabolic activity and ion transport. In addition, the study shows that the appropriate regulation of tyrosine kinase protein phosphorylation, and its downstream signal transduction pathway, plays an important role on renal growth in the NH4Cl-treated rats.

Biochemical responses of two erythrinidae fish to environmental ammonia.

The non-ionized form of ammonia is very toxic to many aquatic species. It is especially important in several aspects of fish biology. A large range of organismal strategies for coping with environmental stressors is usually observed in living organisms. Among those, the responses for managing chemical stressors are well studied. The present work compares biochemical responses of two evolutionarily close species, Hoplias malabaricus and Hoplerythrinus unitaeniatus, exposed to environmental ammonia. Adult fish were submitted to 1.0 mg/L of ammonium chloride for 24 hours, and plasma ammonia and urea levels were determined. The activities of OUC enzymes OCT and ARG, and the accessory enzyme GS, were quantified in liver extract and are expressed below in mumol/min/mg of wet tissue. Increases in OUC enzymes (GS from 1.14 to 2.43, OCT from 0.81 to 1.72, and ARG from 3.15 to 4.23), plasma ammonia (from 0.95 to 1.42 mmol/L), and plasma urea (from 0.82 to 1.53 mmol/L) were observed (p < 0.05) in H. malabaricus exposed to 1 mg/L of ammonia chloride. The GS in H. unitaeniatus increased from 1.43 to 1.84, however the OCT, ARG, and plasma urea from H. unitaeniatus did not change. These data indicate that each species responds differently to the same environmental stressor.