Molecular mechanisms of large-conductance ca (2+) -activated potassium channel activation by ginseng gintonin.

Gintonin is a unique lysophosphatidic acid (LPA) receptor ligand found in Panax ginseng. Gintonin induces transient [Ca(2+)]i through G protein-coupled LPA receptors. Large-conductance Ca(2+)-activated K(+) (BKCa) channels are expressed in blood vessels and neurons and play important roles in blood vessel relaxation and attenuation of neuronal excitability. BKCa channels are activated by transient [Ca(2+)]i and are regulated by various Ca(2+)-dependent kinases. We investigated the molecular mechanisms of BKCa channel activation by gintonin. BKCa channels are heterologously expressed in Xenopus oocytes. Gintonin treatment induced BKCa channel activation in oocytes expressing the BKCa channel α subunit in a concentration-dependent manner (EC50 = 0.71 ± 0.08 µg/mL). Gintonin-mediated BKCa channel activation was blocked by a PKC inhibitor, calphostin, and by the calmodulin inhibitor, calmidazolium. Site-directed mutations in BKCa channels targeting CaM kinase II or PKC phosphorylation sites but not PKA phosphorylation sites attenuated gintonin action. Mutations in the Ca(2+) bowl and the regulator of K(+) conductance (RCK) site also blocked gintonin action. These results indicate that gintonin-mediated BKCa channel activations are achieved through LPA1 receptor-phospholipase C-IP3-Ca(2+)-PKC-calmodulin-CaM kinase II pathways and calcium binding to the Ca(2+) bowl and RCK domain. Gintonin could be a novel contributor against blood vessel constriction and over-excitation of neurons.

Preparation of monoclonal antibody against ginsenoside Rf and its enzyme immunoassay.

A rapid and sensitive indirect competitive enzyme immunoassay method has been developed for quantitating ginsenoside Rf (Rf) in crude total Panax ginseng saponins and in rat plasma using high titer mouse monoclonal antibody (mAb) raised against a conjugate of Rf and bovine serum albumin (BSA). The isotype of mAb against Rf was IgG3 with a K chain. The presence of Rf inhibited the binding of the mouse anti-Rf mAb to a Rf-BSA solid phase coating antigen. The working range was 0.01-10 ng/assay and detection limits were 20 pg in various ginseng extract fractions or 34 pg in rat plasma per assay. The anti-Rf mAb cross-reacted with ginsenoside Rg2 by 57.5%, but not with other ginsenosides. However, this anti-Rf mAb did not cross-react with BSA or cellubiose, which is a carbohydrate component of Rf. Using this standard curve, we could measure the amount of Rf in ginseng total extract, ginseng total saponins, protopanaxadiol saponins, and propanaxatriol saponins. We could also measure the amount of Rf in rat plasma after the oral administration of Rf and found that Rf reached a maximum level in rat plasma after 16 h. These results indicate that the anti-Rf mAb could be useful for the quantitation of Rf in crude ginseng fractions and in body fluids.

Calcium influx and activation of calpain I mediate acute reactive gliosis in injured spinal cord.

Buffering extracellular pH at the site of a spinal cord crush-injury may stimulate axonal regeneration in rats (1; Guth et al., Exp. Neurol. 88: 44-55, 1985). We demonstrated in cultured astrocytes that acidic pH initiates a rapid increase in immunoreactivity for GFAP (GFAP-IR), a hallmark of reactive gliosis (2; Oh et al., Glia 13: 319-322, 1995). We extended these studies by investigating the effects of certain treatments on reactive gliosis developing in situ in a rat spinal cord injury model. A significant reactive gliosis was observed within 2 days of cord lesion in untreated crush or vehicle-treated, crush control animals as evidenced by increased GFAP-IR and hypertrophy of astrocytes. By contrast, infusion of Pipes buffer (pH 7.4) into the lesion site significantly reduced this increase. The increased GFAP-IR appeared to be linked to Ca2+ influx since infusion of a blocker of L-type calcium channels, nifedipine, reduced the ensuing reactive gliosis significantly. While Ca2+ modulates many signaling pathways within cells, its effect on reactive gliosis appeared to result from an activation of calpain I. Calpain inhibitor I, a selective inhibitor of mu-calpain, also significantly reduced reactive gliosis. However, calpain inhibitor II, a close structural analog which blocks m-calpain, had no salutary effect. We suggest, therefore, that the initial reactive gliosis seen in vivo may result from the activation of a neutral, Ca2+-dependent protease, calpain I, through calcium influx.