Abnormal cardiac rhythm in diabetic rats

A significant occurrence of abnormal rhythm was observed in perfused working hearts of diabetic rats. The incidence of arrhythmias was 19/51 in diabetics as compared with 2/38 in normal controls. In considering possible pathogenetic mechanisms, conduction system defects appear to merit particular attention.     

Influence of intracellular pH on mitochondrial calcium during ischaemia of the isolated rat heart

Summary Under physiological conditions cardiac mitochondria seem to play a minor role in maintaining intracellular Ca²⁺ homoeostasis. However, under conditions of cellular Ca²⁺ overload, mitochondria may accumulate large amounts of Ca²⁺. Using transmission and analytical electron microscopy we investigated, in globally ischaemic rat heart preparations, the influence of intracellular pH on the development of Ca²⁺-containing intramitochondrial inclusions. We confirmed that under these experimental conditions Ca²⁺ was a major element of mitochondrial inclusions. The size of these inclusions increased with external Ca²⁺ concentration. An intracellular alkalinization, produced by addition of 20mm NH₄Cl to the perfusate prior to ischaemia, inhibited the formation of such inclusions. On the other hand, a pre-ischaemic intracellular acidification, produced by the addition and subsequent withdrawal of the 20mm NH₄Cl, increased the number of inclusions present at the end of an ischaemic episode. The presence of amiloride (10^–3 m), prior to and during ischaemia, increased the number of inclusions. These data suggest that cytoplasmic pH may be an important factor in mitochondrial Ca²⁺ accumulation in pathological conditions.     

The presence of arginine may be a source of false positive results in the Ames test

An increase in the number of revertant colonies in the Ames test is generally taken as a strong indication of mutagenic activity of a test compound. However, irrelevant positive findings may constitute a major problem in regulatory drug testing. In this study, mixtures containing only amino acids such as glycine, lysine, arginine and isoleucine, routinely used as peptide preservatives in polypeptide pharmaceutical products, were investigated for mutagenesis in the Ames Salmonella typhimurium test. The results demonstrated that in the presence of metabolic activation, all the solutions containing arginine induced an increase in the number of revertant colonies in strains TA98, TA100 and TA1535 compared with the solvent control. More specifically, for strain TA98, all arginine doses tested, i.e. from 0.4 to 8 mg/plate induced a statistically significant increase in the number of revertants. This increase was biologically significant from 1.2 to 8 mg/plate. For strain TA100, the five highest test doses, i.e. from 1.2 to 8 mg/plate, induced statistically and biologically significant increases in the number of revertants. A statistically significant increase in colony number was also observed in strain TA1535, but only at the maximal test dose of 8 mg/plate arginine. These increases were observed with arginine from two different sources, suggesting that the observed effect would not be due to the presence of potential impurities in the type of arginine used. Our findings show that a functional metabolic activation system was required to induce an increase in the number of colonies. The presence of vitamin C inhibited the arginine-induced increase in the number of revertant colonies in S. typhimurium strain TA98, suggesting a potential involvement of oxidative stress.     

Cloning and characterization of a human electrogenic Na+-HCO-3 cotransporter isoform (hhNBC)

Our group recentlycloned the electrogenicNa⁺-HCO₃cotransporter (NBC) from salamander kidney and later from mammaliankidney. Here we report cloning an NBC isoform (hhNBC) from a humanheart cDNA library. hhNBC is identical to human renal NBC (hkNBC),except for the amino terminus, where the first 85 amino acids in hhNBCreplace the first 41 amino acids of hkNBC. About 50% of the amino acidresidues in this unique amino terminus are charged, compared with~22% for the corresponding 41 residues in hkNBC. Northern blotanalysis, with the use of the unique 5' fragment of hhNBC as aprobe, shows strong expression in pancreas and expression in heart andbrain, although at much lower levels. InXenopus oocytes expressing hhNBC,adding 1.5% CO₂/10 mMHCO₃ hyperpolarizes the membrane andcauses a rapid fall in intracellular pH(pH_i), followed by apH_i recovery. Subsequent removalof Na⁺ causes a depolarization anda reduced rate of pH_i recovery.Removal of Cl from the bathdoes not affect the pH_i recovery.The stilbene derivative DIDS (200 µM) greatly reduces thehyperpolarization caused by addingCO₂/HCO₃.In oocytes expressing hkNBC, the effects of addingCO₂/HCO₃and then removing Na⁺ were similarto those observed in oocytes expressing hhNBC. We conclude that hhNBCis an electrogenicNa⁺-HCO₃cotransporter and that hkNBC is also electrogenic.