Inhibitory and excitatory neurotransmitters in the cerebrospinal fluid of epileptic dogs.

OBJECTIVE: To determine concentrations of excitatory and inhibitory amino acids in CSF of a large number of dogs with idiopathic epilepsy or genetic epilepsy and to evaluate changes in CSF amino acid concentration with regard to drug treatment and sex. ANIMALS: 35 Labrador Retrievers with genetic epilepsy (20 male and 15 female), 94 non-Labrador Retrievers with idiopathic epilepsy (71 male and 23 female), and 20 control dogs (10 male and 10 female). PROCEDURE: Collection of CSF was performed > 72 hours after the occurrence of seizures. Cerebrospinal fluid concentrations of gamma-aminobutyric acid (GABA), glutamate (GLU), aspartate (ASP), serine, and glycine were determined by use of high performance liquid chromatography with electrochemical detection. RESULTS: CSF concentrations of GABA and GLU were significantly lower in Labrador Retrievers with genetic epilepsy (LR-group dogs) than in control-group dogs or in non-Labrador Retrievers with idiopathic epilepsy (non-LR-group dogs). The GLU-to-GABA ratio was significantly higher in LR-group dogs than in non-LR-group dogs. CSF concentrations of GLU and ASP were significantly lower when all dogs with epilepsy (non-LR- and LR-group dogs combined) were compared with control-group dogs. CONCLUSIONS AND CLINICAL RELEVANCE: A decrease in CSF concentrations of GABA appears to play a role in the pathogenesis of genetically determined epilepsy in Labrador Retrievers. However, this decrease in CSF concentrations of GABA may also be a consequence of seizure activity. The GLU-to-GABA ratio may prove to be a useful indicator of genetic epilepsy in Labrador Retrievers.

Molecular cloning and functional characterization of a unique mammalian cardiac Na(v) channel isoform with low sensitivity to the synthetic inactivation inhibitor (-)-(S)-6-amino-alpha-[(4-diphenylmethyl-1-piperazinyl)-methyl]-9H-purine-9-ethanol (SDZ 211-939).

Cardiac voltage-dependent sodium channels (Na(v)) are drug targets for synthetic inactivation inhibitors typified by (+/-)-4- [3-(4-diphenylmethyl-1-piperazinyl)-2-hydroxy propoxy]-1H-indole-2-carbonitrile (DPI 201-106), of which the molecular mode of action is not yet defined. The previous observation by Mevissen and coworkers in 2001 of the electrophysiological ineffectiveness of DPI 201-106 in the bovine heart, in contrast to other species, offers the opportunity for investigating these open questions. We now report about the molecular cloning, expression in Xenopus laevis oocytes, and electrophysiological characterization of a unique bovine heart sodium channel. Although the predicted 2022-amino acid bovine heart sodium channel (bH1) shares 92% identity with the rat and human isoforms and normal gating properties, it displays drastically reduced sensitivity to (-)-(S)-6-amino-alpha-[(4-diphenylmethyl-1-piperazinyl)-methyl]-9H-purine-9-ethanol (SDZ 211-939). Experimental results with Anemonia sulcata toxin II (0.1-2.5 microM) exclude the possibility of an overall insensitivity of this isoform to various sodium channel modulators. The binding of SDZ 211-939 seems to be largely unaffected (EC(50) of 10.3 and 10.6 microM for bovine and rat isoforms, respectively) but the corresponding efficacy in bovine (V(m) of 0.15) is approximately 5 times smaller compared with the rat heart isoform (V(m) of 0.69). The comparison of the primary structure of bH1 to other sodium channels and the gating properties obtained in presence or absence of SDZ 211-939 revealed a high degree of similarity. Whether the mechanism of channel modulation depends on the interaction of synthetic modulators with some possibly voltage-independent part of the inactivation machinery needs to be determined.

Inhibition of human and pig ureter motility in vitro and in vivo by the K(+) channel openers PKF 217-744b and nicorandil.

The relaxing property of the K(+) channel opener and nitric oxide donor nicorandil and the new K(+) channel opener PKF 217-744b was investigated on isolated human ureteral tissue in vitro and in intact ureters of anesthetized pigs in vivo. In addition, nicorandil and its antagonists, glibenclamide and methylene blue, were tested on isolated pig ureter tissue in vitro. Nicorandil decreased the frequency of spontaneous contractions in isolated pig ureter rings. This effect was antagonized by glibenclamide and methylene blue suggesting that the nicorandil induced relaxation of the ureter is mediated by activation of ATP-sensitive K(+) channels and involvement of soluble guanylate cyclase. Moreover, nicorandil and PKF 217-744b reduced the amplitude of electrically induced contractions in isolated human ureter rings. Calculations of EC(50) values showed that PKF 217-744b [EC(50) = 4.83 x 10(-8) M] was more potent than nicorandil [EC(50) = 4.38 x 10(-5) M]. Both drugs reduced the contraction frequency of the pig ureter after intravenous and topical administration in vivo. Intravenous, but not topical, administration of nicorandil and PKF 217-744b significantly decreased arterial blood pressure but did not affect the heart rate. The in vitro findings suggest that K(+) channel opening and nitric oxide release mediate the effect of nicorandil. Our in vivo results indicate that PKF 217-744b and nicorandil are promising drugs for clinical application in patients with acute stone colic to relieve obstruction and facilitate stone passage or to relax the ureter before ureteroscopy.