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The cortical bones of mammals, birds, and reptiles are composed of a complex of woven bone and lamellar bone (fibrolamellar bone) organized into a variety of different patterns; however, it remains unclear whether amphibians possess similar structures. Importantly, to understand the evolutionary process of limb bones in tetrapods, it is necessary to compare the bone structure of amphibians (aquatic to terrestrial) with that of amniotes (mostly terrestrial). Therefore, this study compared the cortical bones in the long bones of several frog species before and after metamorphosis. Using micro‐computed tomography (CT), we found that the cortical bones in the fibrolamellar bone of Xenopus tropicalis (Pipoidea superfamily) and Lithobates catesbeianus (Ranoidea superfamily) froglets are dense, whereas those of Ceratophrys cranwelli (Hyloidea superfamily) are porous. To clarify whether these features are common to their superfamily or sister group, four other frog species were examined. Histochemical analyses revealed porous cortical bones in C. ornata and Lepidobatrachus laevis (belonging to the same family, Ceratophryidae, as C. cranwelli). However, the cortical bones of Dryophytes japonicus (Hylidae, a sister group of Ceratophryidae in the Hyloidea superfamily), Microhyla okinavensis (Microhylidae, independent of the Hyloidea superfamily), and Pleurodeles waltl, a newt as an outgroup of anurans, are dense with no observed cavities. Our findings demonstrate that at least three members of the Ceratophryidae family have porous cortical bones similar to those of reptiles, birds, and mammals, suggesting that the process of fibrolamellar bone formation arose evolutionarily in amphibians and is conserved in the common ancestor of amniotes. [ABSTRACT FROM AUTHOR]

To characterize the nature of NaCl transport in the thin ascending limb (tAL), we examined the transport properties of [Na.sup.+] and [Cl.sup.-] using in vitro microperfusion of the tAL in CLC-K1 null mice. In the presence of a transmural NaCl concentration gradient (100 mM higher in the lumen), the transepithelial diffusion voltage ([V.sub.d]) was 15.5 [+ or -] 1.0 and -7.6 [+ or -] 1.4 mV in CLC-K[1.sup.+/+] and CLC-K[1.sup.-/-] mice, respectively. Neither [Cl.sup.-] transport inhibitor 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) nor acidification of the bathing fluid changed the [V.sub.d] values in CLC-K[1.sup.-/-] mice. The addition of 300 [micro]g/ml protamine, a selective blocker of paracellular conductance, to the bath increased the [V.sub.d] values by 5.6 [+ or -] 0.7 and 12.6 [+ or -] 1.5 mV (P < 0.001) in CLC-K[1.sup.+/+] and CLC-K[1.sup.-/-] mice, respectively. Although efflux coefficients of [sup.36]Cl were significantly decreased in CLC-K[1.sup.-/-] mice (188.3 [+ or -] 25.6 in 4 tubules vs. 17.2 [+ or -] 7.0 x [10.sup.-5] cm/s in 6 tubules), those of [sup.22]Na were not different between CLC-K[1.sup.+/+] and CLC-K[1.sup.-/-] mice. These results clearly indicate that the major component of Cl-transport sensitive to NPPB or pH is mediated by CLC-K1 in the tAL. gene targeting; renal medulla; urine-concentrating mechanism; chloride channel; paracellular shunt pathway; sodium chloride

The intracellular calcium ion (Ca2+) and calmodulin play an important role in control of insulin-stimulated NaCl transport in the medullary thick ascending limb (MTAL). Influx of extracellular Ca2+ does not affect the NaCl transportation, however. An experiment is conducted on rabbit MTAL and vitro microperfusion methods are used. Cytosolic free Ca2+ is not significantly affected by insulin.

A study on the mechanism of Ca(super 2+) transport in the luminal and basolateral membranes of ascending thin limb of Henle's loop (ATL) cells shows that the luminal membrane is essentially impermeable to Ca(super 2+) and that the basolateral membranes of the ATL possesses a calmodulin-sensitive Ca(super 2+)-adenosinetriphosphatase {Ca(super 2+ -ATPase)} and a dihydropyridine-sensitive Ca(super 2+) entry pathway. The Ca(super 2+) entry pathway found in the ATL is also sensitive to the membrane voltage.

Intracellular hydrogen ion (pHi) processes in the in vitro microperfused hamster ascending thin limb (ATL) of Henle's loop are investigated using fluorescent pH indicator 2,'7'-bis (carboxyethyl)-5(6)-carboxyfluorescein. The investigation reveals that pHi is regulated by several other regulatory processes such as the NEM-sensitive proton pump and H+-K+- adenosinetriphosphatase.

An analysis of the direct tubular effect of insulin on NaCl exchange in isolated microperfused medullary thick ascending limb of Henle's loop of rabbit kidney at various concentrations of insulin reveals that insulin activates NaCl reabsorption. Insulin effect is independent of the adenylate cyclase-adenosine 3',5'-cyclic monophosphate system in the cell, and does not affect the properties of the paracellular shunt pathway.