Gabapentin activates ROMK1 channels by a protein kinase A (PKA)-dependent mechanism.

BACKGROUND AND PURPOSE: Gabapentin is an effective anticonvulsant. The major physiological function of renal outer medullary potassium (ROMK1) channels is to maintain the resting membrane potential (RMP). We investigated the effect of gabapentin on ROMK1 channels and the mechanism involved. EXPERIMENTAL APPROACH: Xenopus oocytes were injected with mRNA coding for wild-type or mutant ROMK1 channels and giant inside-out patch-clamp recordings were performed. KEY RESULTS: Gabapentin increased the activity of ROMK1 channels, concentration-dependently and enhanced the activity of wild-type and an intracellular pH (pH(i))-gating residue mutant (K80M) channels over a range of pH(i). Gabapentin also increased activity of channels mutated at phosphatidylinositol 4,5-bisphosphate (PIP(2))-binding sites (R188Q, R217A and K218A). However, gabapentin failed to enhance channel activity in the presence of protein kinase A (PKA) inhibitors and did not activate phosphorylation site mutants (S44A, S219A or S313A), mutants that mimicked the negative charge carried by a phosphate group bound to a serine (S44D, S219D or S313D), or a mutated channel with a positive charge (S219R). These findings show that gabapentin activates ROMK1 channels independently of the pH(i) and not via a PIP(2)-dependent pathway. The effects of gabapentin on ROMK1 channels may be due to a PKA-mediated phosphorylation-induced conformational change, but not to charge-charge interactions. CONCLUSIONS AND IMPLICATIONS: ROMK1 channels are the main channels responsible for maintaining the RMP during cellular excitation. Gabapentin increased the activity of ROMK1 channels by a PKA-dependent mechanism, reducing neuronal excitability, and this may play an important role in its antiepileptic effect.

Reproductive outcomes and infant health in adolescent pregnancy in Taichung city.

The study aimed at determining the reproductive outcomes, caregiving condition, and children's growth and development compared to those born to adult mothers. All adolescent mothers ages less than 20 years and their first born infants matched with adults mothers aged 20-29 years and their first born infants at the same neighborhoods in Taichung city in 1997 were included in this study. The results showed that there is no significant difference between children of adolescent mothers and of adult mothers in terms of the prevalence of prematurity and congenital diseases, but the children of teenage mothers have a significantly higher prevalence of low birth weight (adjusted odds ratio = 1.61, 95% CI = 1.21-2.80) than those of compared mothers. Multiple logistic regression was used to find out the risk factors for low birth weight, and found that maternal weight gain and hospitalization or not during pregnancies in mothers are significant risk factors for low birth weight. We can not find difference between the two groups in caregiving condition, such as breast feeding duration, accidental injury, diseases necessitating admission, and vaccination rates. Also there is no difference in the rate of failure to thrive or delayed developmental milestones. A long-term follow-up study on the prognosis for the adolescent mothers and their children is recommended.

Fat necrosis after trauma: a benign cause of palpable lumps in children.

OBJECTIVE: Our objective is to describe the clinical entity and MR imaging appearance of fat necrosis after trauma, a benign cause of palpable soft-tissue lesions in children. A related objective is to establish MR imaging criteria that can be used reliably to differentiate this entity from other more serious causes of soft-tissue masses. CONCLUSION: Fat necrosis after trauma is a common cause of palpable lumps in children and has a benign course on long-term follow-up. When characteristic MR imaging findings are seen, conservative therapy is appropriate.

Right ventricular myxoma in a 12-year-old child: a case report.

Cardiac myxoma especially of the right ventricle, is rare in children. A 12-year-old boy with right ventricle myxoma is reported. His heart murmur was found incidentally when he visited the Outpatient Department (OPD) because of upper respiratory infection symptoms. There was no exertional dyspnea, no palpitation, no syncope and no skin lesion. The echocardiogram revealed a heart tumor of about 4 x 3 cm in the right ventricle (RV) extending to the right atrium (RA). The tumor grew from the interventricular septum, resulting in an RV outlet and inlet obstruction. Magnetic resonance image (MRI) revealed a well-defined mass in the RV ventricle, with good enhancement after injecting a contrast medium. The patient received right atriotomy and total excision of the tumor with repairing of the interventricular septum base. Pathology revealed myxoma with gelatinous whitish color and central hemorrhage. At post-operative follow-up, the patient's condition was good.

Effects of neuroactive agents on the isolated heart activities of marine bivalve Meretrix lusoria.

By recording method, we measured simultaneously both the contractile force (CF) and the action potential (AP) of the isolated heart to confirm the chief cardioregulatory transmitters of a marine bivalve. The effects of several neuroactive agents on CF, HR and the amplitude of AP in marine bivalve were investigated. Acetylcholine and carbachol produced inhibitory effects on the heart performance at 1.0 x 10(-11) M. Choline also exhibited inhibitory effects at a higher concentration, but atropine, curare, pilocarpine and hexamethonium bromide (all at 1.0 x 10(-4) M) exerted no significant effects on the spontaneous cardiac activities. 5-HT and 8-OH-DPAT produced positive chronotropic and inotropic effects on the heart at 1.0 x 10(-8) M, whereas adrenaline and dopamine were positively inotropic at 1.0 x 10(-5) M. The perfusion of adrenaline or dopamine typically prolonged the plateau duration of the action potential, and then enhanced CF. However, histamine, GABA and PGF2 alpha all exerted no significant effect on either CF or the amplitude of AP of the isolated heart. The results indicate that 5-HT and acetylcholine are excitatory and inhibitory agents, respectively, that regulate the isolated cardiac performance in a marine bivalve. The mechanism of positively inotropic effects of biogenic amines is discussed.

Rapid separation and quantitation of mixed microorganisms by filtration and bioluminescence.

A membrane filtration/bioluminescence system was developed for the differentiation and quantitation of mixed populations of microorganisms. Samples containing microorganisms were filtered through two membrane filters of descending pore size. The microorganisms retained on the filter contain ATP that can be extracted and measured on the filter via the firefly luciferase-luciferin bioluminescence assay. Results, obtained in less than 20 min, show a good correlation (r greater than or equal to 0.95) between the light produced and the number of organisms in the sample. Using these techniques, Escherichia coli can be separated from yeast or mold and measured in samples containing both microorganisms. When lysostaphin is used to selectively lyse Staphylococci on the filter, the specific quantification of these bacteria among other microorganisms can also be accomplished. The filtration/bioluminescence technique offers the potential of being a rapid and sensitive method to differentiate and detect microorganisms, by selective sizing or lysing, in a variety of samples.

Separation of bacterial luciferase from oxidoreductases by affinity chromatography.

The NADH-dependent and NADPH-dependent oxidoreductase activities associated with bacterial luciferase in Vibrio (Beneckea) harveyi can simultaneously be removed from purified luciferase through a Blue Sepharose CL-6B column. The result achieved with this one-step affinity chromatography is similar to that obtained with two sequential "reverse-affinity" chromatographies.

Estrogen and antiestrogen action: studies in reproductive target tissues and tumors.

Studies are reported using unlabelled and radiolabelled antiestrogens which are aimed at elucidating the nature of interaction of antiestrogens with uterine and mammary tissue. Antiestrogens and long-acting estrogens move estrogen receptor sites to the nucleus and maintain elevated nuclear receptor levels for a prolonged period. The antagonistic action of antiestrogens in the uterus, however, appears to derive from their ability to effect a marked perturbation in the subcellular distribution of receptor whereby very little (ca. 10%) is cytoplasmic and further estrogen receptor accumulation is blocked. In DMBA-induced rat mammary tumors, the nonphototoxic antiestrogen, U-23, 469, effectively antagonizes the development and growth of tumors and elicits regression of 90% of established tumors with a time course similar to that seen after ovariectomy. Again, during antiestrogen treatment, the levels of cytoplasmic estrogen receptor are depressed with over 90% of total receptor being found in the nucleus. Two radiolabelled antiestrogens of high specific activity and purity have been prepared by us and their interaction with nuclear and cytoplasmic estrogen receptors is reported. Both 3H-CI-628 and 3H-U-23, 469 are metabolized in vivo to more polar forms which are found associated with the nuclear estrogen receptor, and which may be the true agents active in vivo.