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L J Alvarez

Publications and source records attributed to L J Alvarez.

26 records · Page 2Linked to original sources
PubMed1989

Stimulation of toad lens epithelial Na+/H+ exchange activity by hypertonicity.

Incubation of toad lenses with the acetoxymethyl ester of 2',7'-biscarboxyethyl-5(6)-carboxy-fluorescein led to a highly selective accumulation of the de-esterified, pH-sensitive form of the dye in the epithelial cells, enabling the continuous fluorometric monitoring of epithelial intracellular pH (pHi) in intact lenses. The effects of changes in extralenticular [Na+] and of amiloride-addition indicated that the epithelium contains an amiloride-sensitive Na+/H+ antiport. Exposure of lenses to hypertonic conditions (by the addition of sucrose to the medium) resulted in a biphasic change in pHi; a rapid initial, 'spike-like' decrease was immediately followed by a persistent reversal that raised pHi in CO2/HCO3- -rich and -free media by 0.13 and 0.18 units, respectively. Under CO2/HCO3- -free conditions, the hypertonic exposure raised pHi to a value near the calculated equilibrium position for a lens Na+/H+ exchanger. At this point, monensin addition did not affect pHi, suggesting that the tonicity shift had induced a rapid endogenous Na+/H+ exchange activity. In contrast, in the presence of 1 mM amiloride or in the absence of extralenticular Na+, sucrose addition induced only a persistent pHi decrease, which could be reversed (in the 'amiloride' case) by monensin addition. These results demonstrate that the hypertonic exposure induced an epithelial cell acidification as well as a stimulation of the Na+/H+ exchange activity which reverted the acidification. The hypertonic exposure also elicited pHi increases in lenses that had been preacidified by the 'NH4+ loading' or 'pCO2 raise' methods, indicating that the onset of the stimulation could not be attributed to a pHi decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Cellular pH and Na+-H+ exchange activity in lens epithelium of Bufo marinus toad.

Incubation of lenses with the acetoxymethyl ester of 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF-AM) led to selective, prolonged entrapment of the deesterified, pH-sensitive, membrane-impermeable form of the dye (BCECF) in the lens epithelial cells allowing, thereby, for the continuous fluorometric monitoring of epithelial intracellular pH (pHi) in intact lenses. Under anaerobic conditions in physiological solution, the epithelium maintained a pHi of 7.36 +/- 0.14 (mean +/- SD, n = 6 lenses). In the absence of CO2 and HCO3-, the pHi increased to 7.83 +/- 0.38 (n = 55). In this condition, either the removal of Na+ or the addition of amiloride to the medium resulted in a decrease of pHi. This acidification was increased in amiloride-inhibitable fashion when lenses were loaded with Na+ before extracellular Na+ removal. The extent of artificially generated cellular acidosis (induced by the "NH4+ loading" technique) was markedly decreased by the presence of extracellular Na+ or reverted on its addition when the ion was initially absent; the latter reversal was inhibited by amiloride. This inhibition was by-passed by monensin addition. The existence of a Na+-H+ antiport in the epithelial cells is concluded.

Animals↗
PubMed1985

Na+-K+ ATPase distribution in frog and bovine lenses.

Na+-K+ ATPase activity was measured in the capsule-epithelium and decapsulated frog and bovine lens. The decapsulated lens contained approximately 20% of the whole lens activity in the frog and 30% in the bovine. These values were measured from the aqueous homogenate of the entire decapsulated lens, an approach which may have underestimated the activity by diluting the ouabain-sensitive component in the preparation. Subsequent determinations were done on separate portions of superficial (2 to 3 mm) anterior-equatorial, and posterior bovine cortex. The activities per gram of tissue were enriched with respect to the values for the entire decapsulated bovine lens. These activities were further enriched by a sucrose density gradient centrifugation. The anterior-equatorial cortical segment contained 1.6 times the activity found in the capsule-epithelium. The posterior cortex had a much smaller but statistically significant level of Na+-K+ ATPase. It is unlikely that the observed asymmetry of the anterior-equatorial segment with the posterior cortex is exclusively due to epithelial contamination for the result would require the adherence of 62% of the epithelium. Scanning electron micrographs of 6 decapsulated bovine lenses indicated an average contamination of about 9%. This asymmetry may have a physiological role in assisting the pump mechanism of the epithelium.

Animals↗
PubMed1980

Inhibition of ionic transport and ATPase activities by serotonin analogues in the isolated toad lens.

The effects of serotonin and five other indoles were tested on the electrical parameters and ionic transport in the isolated toad lens. Serotonin, tryptophan and 5-hydroxy-L-tryptophan did not affect the electrical parameters of the lens at concentrations as high as 1 mM. Tryptamine, 5-methyltryptamine and 5-methoxytryptamine had dual effects: 1 mM in the posterior bathing solution depressed the potential difference of the posterior face of the lens, which resulted in an increase in the translenticular potential difference and short-circuit current; 1 mM in the anterior solution (in contact with the lens epithelium) produced a quick and pronounced reduction of the potential difference of the anterior face. This resulted in a 90-100% decline of the translenticular short-circuit current. Serotonin and tryptamine were then tested for their effect on the ATPases of lens epithelium. Both amines inhibited the enzymes with tryptamine at 5 mM completely inhibiting all ATPase activity. Since tryptophan is transported from the aqueous humor into the lens and may be converted by lens enzymes to serotonin and tryptamine, these findings may have physiological implications in cataractogenesis.

5-Hydroxytryptophan↗
PubMed1979

5'-Nucleotidase levels in normal and virus-transformed cells: implications for cellular aging in vitro.

5'-Nucleotidase activity in the postnuclear supernatant of normal and SV-40 virus-transformed human embryonic lung, chick embryo, and mouse embryo fibroblasts, WI-38, IMR-90, VA-13, CEF, 3T3, and SV3T3 cells was measured. In IMR-90 and CEF cells, both of which have a limited lifespan in vitro, 5'-nucleotidase activity increased 6- and 20-fold, respectively, with increasing population doublings. However, VA-13 cells, a permanent cell line, showed no increase in this enzyme activity with progressive population doublings. 5'-Nucleotidase activity was not detectable in two other permanent cell lines, 3T3 and SV3T3 cells. Of the six cell lines tested, the conspicuous enhancement in 5'-nucleotidase activity with increasing population doublings was observed only in normal cell lines and was absent in transformed cell lines. These observations suggest a molecular mechanism which may play a role in aging of normal cells in vitro and which may involve catabolism of nucleic acids.

Adenosine Monophosphate↗