Histochemical measurements of rat kidney hexokinase

Regulation of mesangial cell hexokinase activity by PKC and the classic MAPK pathway

Phorbol esters increase glucose (Glc) uptake and utilization in a variety of cell types, and, in some cells, these changes have been attributed to increased Glc phosphorylation and better functional coupling of hexokinases (HKs) to facilitative Glc transporters. Phorbol esters are potent mesangial cell mitogens, but their effects on HK-catalyzed Glc phosphorylation and metabolism are unknown. When examined in murine mesangial cells, active, but not inactive, phorbol esters increased HK activity in a time- and dose-dependent manner. Maximal induction of HK activity at 12-24 h was accompanied by parallel increases in both Glc utilization and lactate production and was blocked by the specific MEK1/2 inhibitor PD-98059 (IC(50) approximately 3 microM). This effect involved early activation of protein kinase C (PKC), MEK1/2, and ERK1/2, and the prolonged time course of subsequent HK induction was attributable, in part, to requirements for ongoing gene transcription and de novo protein synthesis. Mesangial cell HK activity thus exhibits novel regulatory behavior involving both PKC and classic MAPK pathway activation, suggesting specific mechanisms whereby PKC activation may influence Glc metabolism.

Developmental aspects of transcription of fructose-1,6-bisphosphatase in newborn dogs

Our previous investigations demonstrated that unsuppressed gluconeogenesis under hyperinsulinemia in newborn dogs may be a mechanism of neonatal hyperglycemia. In the present study, the transcription of the gene for fructose-1,6-bisphosphatase (fru-1,6-P2ase; E 3.1.3.11) of newborn dogs was studied under various metabolic perturbations (age, suckling, fasting, and hyperinsulinemia). Total RNAs isolated from livers and kidneys were hybridized with a rat fru-1,6-P2ase cDNA probe. We observed that (i) fru-1,6-P2ase mRNA was expressed in both kidney and liver at birth and was about 40 and 80% of those in kidney and liver of adult dog, respectively; (ii) suckling decreased the kidney fru-1,6-P2ase mRNA level to 77.8 +/- 1.7% (24 h) from 100.0 +/- 8.0% (4 h), but increased liver mRNA to 158.6 +/- 11.4% (24 h) from 100.0 +/- 2.3% (4 h); (iii) during a 24-h period of fasting, the kidney fru-1,6-P2ase mRNA level did not change in the first 10 h and then increased 18.5% at 24 h, whereas the liver fru-1,6-P2ase mRNA increased ca. 20% during the first 10 h and then up to 161.1 +/- 18.0% at 24 h compared to that at 100.0 +/- 11.4% (0 h); (iv) euglycemic hyperinsulinemia did not change the renal fru-1,6-P2ase mRNA level, but lowered the hepatic fru-1,6-P2ase mRNA level to 56.0 +/- 8.7 from 100.0 +/- 11.8% (fasted controls) in newborn dogs, which was identical to that in adult dogs. These data suggest that the fru-1,6-P2ase in liver may play a more important role in glucose homeostasis of newborn dogs than that in kidney during the first day of their lives and that the incomplete suppression of transcription of the hepatic fru-1,6-P2ase gene by insulin in newborn dogs may not contribute to neonatal hyperglycemia due to insulin resistance.

15-Hydroxyprostaglandin dehydrogenase and hexokinase in spontaneously hypertensive rat kidney

15-Hydroxyprostaglandin dehydrogenase (PGDH) surged in hypertensive (SHR) and normotensive (WKY) rat kidney at 8 days of age, is greatest in SHR. Hexokinase fell in SHR at 17 days of age, but thereafter was similar to WKY. This suggests multisystem enzymatic abnormalities in SHR kidney during development of hypertension.

Histochemical and immunohistochemical localization of hexokinase isoenzymes in normal rat liver

Histochemical and immunohistochemical procedures have been used to examine the localization of three of the four hexokinase isoenzymes present in the liver of fed female Wistar rats. Distinctive distribution patterns were found for hexokinase type I and glucokinase but hexokinase type II was not detectable. Hexokinase type I was identified in sinusoidal cells and in bile duct epithelia, nerves and arteries in the portal triad. Glucokinase, the major isoenzyme, was confined to parenchymal cells where it was present in much higher amounts in perivenous compared with periportal hepatocytes. Staining within these two zones was not homogeneous and each had a mosaic appearance caused by the presence of a few hepatocytes containing little or no glucokinase amongst the majority of darkly stained cells in perivenous areas and a few darkly stained cells amongst the majority of unstained cells in periportal areas. Hence, hepatocytes in situ are a strikingly heterogeneous population of cells. Their metabolic status cannot be controlled simply by the differential supply of oxygen, substrates and hormones to different regions of the liver acini as proposed in the metabolic zonation model. Phenotypic differences may exist between cells within a given metabolic zone which influence their ability to respond to different environmental conditions.

Histochemical and immunohistochemical localization of hexokinase isoenzymes in rat kidney

Histochemical and immunohistochemical staining techniques have been used to investigate the localization of hexokinase isoenzymes within rat kidney tissue. Hexokinase type I was shown to be the major isoenzyme present. It was located mainly in the thin and thick limbs of loops of Henle, in distal tubules and in the transitional or dark cells in the initial portions of collecting ducts. The smooth muscle cells of arteries and arterioles, peripheral nerves and the transitional epithelial cells lining the renal pyramid also contained large amounts of the isoenzyme while smaller quantities were present in glomeruli and in collecting tubules near the papillary tip. The distribution pattern obtained in tubular epithelia agrees well with that demonstrated in earlier microdissection studies. It is also consistent with the suggestion that glycolysis provides the majority of the energy fuelling the sodium transport mechanisms which form such an essential feature of the countercurrent urine concentration system present within the renal medulla.