Localisation of the Vacuolar Proton Pump (V-H+-ATPase) and Carbonic Anhydrase II in the Human Eccrine Sweat Gland

The localisation of the vacuolar proton pump (V-H+ -ATPase) and the enzyme carbonic anhydrase II (CAII) was investigated in the human eccrine sweat gland employing standard immunohistochemical techniques after antigen retrieval using microwave heat treatment and high pressure. The high-pressure antigen retrieval unmasked the presence of V-H+ -ATPase in the clear cells of the secretory coil, with a distribution similar to that previously observed for CAII. However, the dark cells were unreactive to both antibodies. In addition, heat and high-pressure antigen retrieval demonstrated the presence of CAII in the apical zone of luminal cells of the reabsorptive duct, a location not previously reported. The localisation of V-H+ -ATPase and CAII in the secretory coil clear cells suggests that the formation of HCO3- and H+ by carbonic anhydrase II and the transport of H+ by V-H+ -ATPase may play an role in sweat fluid secretion. Their presence at the apex of the duct cells indicates involvement in ductal ion reabsorption.     

Connexin36 forms synapses essential for night vision

Rod signals reach ganglion cells via at least five pathways. A new study in this issue of Neuron shows that all pathways from rods to ON-type ganglion cells require connexin36. This is the first physiological demonstration in mammals that a well-defined neural circuit requires a gap junction as an obligatory transmission step.     

High salt activation of recA protein ATPase in the absence of DNA

The recA protein of Escherichia coli is a DNA-dependent ATPase. In the absence of DNA, the rate of recA protein-promoted ATP hydrolysis drops 2000-fold, exhibiting an apparent kcat of approximately 0.015 min-1. This DNA-independent activity can be stimulated to levels approximating those observed with DNA by adding high concentrations (approximately 2M) of a wide variety of salts. The increase in ATP hydrolysis appears to require the minimal interaction of three to four ions with recA protein. The active species in ATP hydrolysis is an aggregate of recA protein. There appears to be little or no cooperativity with respect to ATP binding (Hill coefficient = 1.0). The salt-stimulated ATP hydrolysis reaction is dependent upon Mg2+ ions and is optimal between pH 7.0 and 8.0. In many respects, the high salt concentration appears to be functionally mimicking DNA in activating the recA protein ATPase.