Chronic treatment with calcitonin in osteoporotic patients alleviates the pain associated with this condition by an unknown mechanism. In ovariectomized rats that develop osteoporosis and hyperalgesia, we examined whether a functional change in serotonergic systems in the spinal dorsal horn was involved, using whole-cell recordings from substantia gelatinosa neurons in spinal cord slices and [(3)H]8-hydroxy-2(di-n-propylamino)tetralin ([(3)H]8-OH-DPAT) binding. Hyperalgesia could be attributed to the elimination of presynaptic inhibition by 5-HT of glutamatergic primary C-afferent terminals and an associated decrease in the density of [(3)H]8-OH-DPAT binding sites whose receptors are neither 5-HT(1A)- nor 5-HT(7)-subtype. These changes in serotonergic systems were restored after chronic treatment with calcitonin. Reversal of 5-HT receptor changes by calcitonin treatment may provide an explanation for its analgesic actions in patients.

V1, a water-soluble portion of vacuole-type ATPase (V-ATPase), is an ATP-driven rotary motor, similar to F1-ATPase. Hydrolysis of ATP is coupled to unidirectional rotation of the central rotor D and F subunits relative to the A3B3 cylinder. In this study, we analyzed the rotation kinetics of V1 in detail. At low ATP concentrations, the D subunit rotated stepwise, pausing every 120°. The dwell time between steps revealed that V1 consumes one ATP per 120°step. V1 generated torque of Ϸ35 pN nm, slightly lower than the Ϸ46 pN nm measured for F1. Noticeably, the angles for both ATP cleavage and binding were apparently the same in V1, in sharp contrast to F1, which cleaves ATP at 80°posterior to the binding of ATP. Thus, the mechanochemical cycle of V1 has marked differences to that of F1.ATP synthase ͉ molecular motor ͉ single molecular analysis ͉ vacuole-type ATPase T he F 0 F 1 -ATP synthase (F)-and vacuole-type (V-type) ATPase͞ATP synthase-superfamily members utilize a rotary mechanism to perform their specific function (1-3). The cytoplasmic portion of F-and V-type ATPases (called F 1 and V 1 , respectively), responsible for ATP hydrolysis͞synthesis, is connected via the central rotor stalk and the peripheral stator stalk to the transmembrane portion (F 0 and V 0 ), housing the iontransporting pathway. The rotation of the central rotor subunits is a key feature of these enzymes in coupling ATP hydrolysis͞ synthesis with ion transport across the membrane. Isolated F 1 is, itself, a well characterized ATP-driven rotary motor that converts a chemical reaction (ATP hydrolysis) into mechanical rotation of the central-shaft subunits (1). Bacterial F 1 is composed of five different subunits with a composition of ␣ 3 ␤ 3 ␥␦. The catalytic site of F 1 is formed at the interface between the ␣ and ␤ subunits, with the majority of the catalytic residues residing in the ␤ subunit. The minimum rotary unit of F 1 is the ␣ 3 ␤ 3 ␥ subcomplex, in which the central ␥ subunit rotates within the ␣ 3 ␤ 3 core by repeating a sequence of (at least) four processes: (i) binding of ATP to a catalytic ␤ subunit, (ii) 80°rotation of the ␥ subunit, (iii) cleavage of ATP and͞or release of hydrolysis product(s), and (iv) 40°rotation of ␥ (4-7). It is notable that F 1 is a reversible motor. When the ␥ subunit of F 1 is rotated in the reverse direction by external force, ATP is synthesized from ADP and phosphate (8,9). It is believed that proton flow through F 0 drives the rotation of the proteolipid ring together with the ␥ subunit in the reverse direction to synthesize ATP in the cell. Recently, proton-powered reverse rotation of the ␥ subunit was observed for F 0 F 1 incorporated into liposomes (10).V-ATPases exist in the endomembranes of all eukaryotic cells and in the plasma membrane of some specific eukaryotic cells and are responsible for a variety of cellular functions (11). The enzyme has also been found in the plasma membrane of some bacteria (12)(13)(14). It is thought that V-ATPase is evolutionarily related to F-ATPase, because sever...

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BackgroundThe polypeptide hormone calcitonin is clinically well known for its ability to relieve neuropathic pain such as spinal canal stenosis, diabetic neuropathy and complex regional pain syndrome. Mechanisms for its analgesic effect, however, remain unclear. Here we investigated the mechanism of anti-hyperalgesic action of calcitonin in a neuropathic pain model in rats.ResultsSubcutaneous injection of elcatonin, a synthetic derivative of eel calcitonin, relieved hyperalgesia induced by chronic constriction injury (CCI). Real-time reverse transcriptase-polymerase chain reaction analysis revealed that the CCI provoked the upregulation of tetrodotoxin (TTX)-sensitive Nav.1.3 mRNA and downregulation of TTX-resistant Nav1.8 and Nav1.9 mRNA on the ipsilateral dorsal root ganglion (DRG), which would consequently increase the excitability of peripheral nerves. These changes were reversed by elcatonin. In addition, the gene expression of the calcitonin receptor and binding site of 125I-calcitonin was increased at the constricted peripheral nerve tissue but not at the DRG. The anti-hyperalgesic effect and normalization of sodium channel mRNA by elcatonin was parallel to the change of the calcitonin receptor expression. Elcatonin, however, did not affect the sensitivity of nociception or gene expression of sodium channel, while it suppressed calcitonin receptor mRNA under normal conditions.ConclusionsThese results suggest that the anti-hyperalgesic action of calcitonin on CCI rats could be attributable to the normalization of the sodium channel expression, which might be exerted by an unknown signal produced at the peripheral nerve tissue but not by DRG neurons through the activation of the calcitonin receptor. Calcitonin signals were silent in the normal condition and nerve injury may be one of triggers for conversion of a silent to an active signal.

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1 We demonstrate that 8-(noradamantan-3-yl)-1,3-dipropylxanthine