Phencyclidine in nanomolar concentrations binds to synaptosomes and blocks certain potassium channels.

Phencyclidine [1-(phenylcyclohexyl)piperidine; PCP], in low dose (approximately equal to 0.1-0.2 mg/kg of body weight), induces a schizophrenia-like behavioral syndrome in man; this effect has been attributed to block of neuronal K channels. We used a K-stimulated 86Rb efflux assay to demonstrate that low concentrations of PCP (10-50 nM) block a class of depolarization-activated K channels in rat brain synaptosomes--pinched-off presynaptic nerve terminals. The dose-response curve is biphasic, and much higher PCP concentrations (greater than 10 microM) are required to block the remainder of the K-stimulated 86Rb efflux. The [3H]PCP binding curve for synaptosomes is also biphasic: PCP binds to some components with high affinity (Kd approximately equal to 6.0 X 10(-8) M), and to other components with much lower affinity (Kd approximately equal to 1.15 X 10(4) M). PCP can be photoactivated with UV light to form covalent bonds: after UV irradiation, previously-bound [3H]PCP is no longer displaceable by a large excess of unlabeled PCP. Preliminary data from NaDodSO4/polyacrylamide gel electrophoresis studies after covalent binding of [3H]PCP to synaptosomes, suggest that the high-affinity binding site may be on a large protein (Mr approximately equal to 220,000). We conclude that the high-affinity PCP binding protein is associated with the K channels that are blocked by nanomolar concentrations of PCP. Block of these channels could, by prolonging action-potential duration in presynaptic nerve terminals, enhance calcium entry and neurotransmitter release, thereby altering transmission at central synapses involved in behavioral expression.

Interactions of phencyclidine with ion channels of nerve and muscle: behavioral implications.

Phencyclidine (1-(1-phenylcyclohexyl)piperidine [PCP]), a behaviorally active analogue (1-(1-m-aminophenylcyclohexyl)piperidine [m-amino-PCP]), and two behaviorally inactive analogues (1-(1-m-nitrophenylcyclohexyl)piperidine and 1-piperidinocyclohexanecarbonitrile) block neuromuscular transmission, depress the amplitude and rate of rise of directly elicited action potentials in frog sartorius muscle, and cause voltage- and concentration-dependent decreases of the peak end-plate current amplitude. This implies that all four compounds block the ion channel of the acetylcholine (ACh) receptors. Only PCP and m-amino-PCP prolong the action potential, block delayed rectification, potentiate muscle twitch, increase quantal content of end-plate potentials, and block K+-induced 86Rb+ efflux from rat brain synaptosomes. PCP also possesses central and peripheral antimuscarinic activity but is much less potent than 3-quinuclidinyl benzilate (QNB). Atropine, scopolamine, and QNB require much higher concentrations to induce behavioral alterations than to block muscarinic receptors. Thus PCP and some of its behaviorally active and inactive derivatives share two common effects, blockade of the nicotinic ACh receptor-ion channel complex and blockade of central and peripheral muscarinic receptors. The feature that apparently separates behaviorally active from inactive derivatives of PCP is their ability to block K+ conductance (gK) and thereby potentiate muscle twitch and increase the release of transmitters from central and peripheral synapses. The similarity between PCP-induced behavioral alterations and primary schizophrenia in humans raises the possibility of involvement of an altered gK in the human disease.

The behavioral effects of phencyclidines may be due to their blockade of potassium channels.

The action of phencyclidine [1-(1-phenylcyclohexyl)piperidine; PCP] and its behaviorally active analog (m-amino-PCP) and of two behaviorally inactive analogs [m-nitro-PCP and 1-piperidinocyclohexanecarbonitrile (PCC)] were examined in this study. In a test of spatial alternation performance in rats, PCP and m-amino-PCP were much more potent behavior modifiers than were PCC and m-nitro-PCP. We studied the effects of the drugs on the ionic channels of the electrically excitable membrane and of the nicotinic acetylcholine (AcCho) receptors at the neuromuscular junction of frog skeletal muscle. All four compounds blocked the indirectly elicited muscle twitch and depressed the amplitude and rate of rise of directly elicited muscle action potentials. They also caused a voltage- and concentration-dependent decrease in the peak amplitude of the endplate current but did not react with the nicotinic AcCho receptor. These observations indicate that the four compounds have comparable blocking effects on the ionic channels associated with the nicotinic AcCho receptor. In contrast, the behaviorally active agents could be distinguished from behaviorally inactive ones by their effects on K+ conductance. PCP and m-amino-PCP blocked delayed rectification in frog sartorius muscles, prolonged the muscle action potential more than 2-fold, and markedly potentiated the directly elicited muscle twitch. The behaviorally active compound also blocked depolarization-induced 86Rb+ efflux from rat brain synaptosomes (presumably a measure of K+ conductance) and increased quantal content at the frog neuromuscular junction. In these actions, m-nitro-PCP was much less effective, and PCC was relatively ineffective. Because PCP and m-amino-PCP are much more potent behavior modifiers than PCC and m-nitro-PCP, we suggest that the behavioral effects of PCP and m-amino-PCP, may be due to a block of K+ conductance and enhancement of transmitter release at central neurons.

Multiple molecular forms of glucose-6-phosphate dehydrogenase in normal, preneoplastic, and neoplastic mammary tissues of mice.

Multiple molecular forms of glucose-6-phosphate dehydrogenase (G6PD) in normal, preneoplastic, and neoplastic mammary tissues were separated by polyacrylamide gel electrophoresis and identified by specific straining for enzyme activity. Mammary tissue from lactating BALB/c mice showed considerable amounts (up to 50%) of a slower-migrating G6PD species, G6PD-III, which was essentially absent from glands of pregnant mice, preneoplastic nodules, and mammary carcinomas. All tissues possessed a faster-migrating species, G6PD-II, which accounted for up to 85% of the total G6PD in the glands of pregnant mice. A third species, G6PD-I, migrating more rapidly than G6PD-II, was found in both abnormal tissues (preneoplastic and neoplastic) and accounted for up to 35% of the total enzymatic activity. G6PD-I was present in moderate amounts (less than 15%) in glands from pregnant mice and was essentially absent from the lactating gland (approximately 5%). The addition of dithiothreitol did not alter the measurable G6PD activity but did increase the relative activity of G6PD-II or G6PD-I, as judged by the intensity of the bands on the gels. Mild oxidation (stirring overnight at 4 degrees in air) resulted in a loss of G6PD activity, but preparations had greater amounts of G6PD-III; presence of dithiothreitol during aeration partially prevented loss of G6PD activity and largely prvented the appearance of G6PD-III. Molecular-weight estimations with preparations from lactating mice yielded a value of 118,000 for G6PD-II and 260,000 for G6PD-III, suggesting a monomer and dimer, respectively. The addition of nicotinamide adenine dinucleotide phosphate stabilized G6PD activity by preventing heat inactivation at 47 degrees; nicotinamide adenine dinucleotide phosphate did not alter the pattern of species present. The data from heat inactivation studies suggest that G6PD-III (dimer) was the more stable species. The addition of nicotinamide adenine dinucleotide phosphate to samples after oxidation in the absence of dithiothreitol (about 70% loss of activity) resulted in no change in patterns and in recovery of full G6PD activity during heating at 47 degrees. A potential relationship between glutathione reductase activity and the pattern of G6PD species observed in the various tissues is noted.

High total histone deoxyribonucleic acid ratios for rat liver nuclei.

The ratios of total histone to DNA for rat liver nuclei isolated by four methods as well as for calf liver nuclei isolated by one method were determined by obtaining the ratios of the total areas of the electrophoretic histone peaks for the liver nuclei to the corresponding total area given by a known amount of standard calf thymus histone. Ratios of total histone to DNA of approx. 2 for rat liver nuclei isolated at pH3.8 or 5.8 and for calf liver nuclei isolated at pH3.8 were confirmed twice by the above procedure and also by direct measurement, by the method of Lowry et al. (1951), of histone extracted in 0.2m-H(2)SO(4). The histones of calf thymus, calf liver and rat liver were characterized by their amino acid compositions and by polyacrylamide-gel electrophoresis.