Cyclic nucleotides in the development of alcohol tolerance and dependence: a commentary

This paper aims to outline some of the caveats inherent in studies on first and second messengers in the central nervous system as related to tolerance and dependence. Analysis of systems based on measures of first and second messengers may be an over-simplification, since the actual molecular consequences of neurotransmission might result in a multilevel cascade of many sequential messages including protein kinase activation and protein phosphorylation and/or dephosphorylation.

Role of intracellular calcium in promoting muscle damage: a strategy for controlling the dystrophic condition

It is suggested that various muscle diseases and examples of experimentally-induced muscle damage arise because of a high calcium level in the myoplasm. When [Ca2+]i is raised experimentally in amphibian or mammaliam muscle by treatment with A23187 or caffeine, myofilament degradation follows quickly. Such a rapid action suggests the involvement of a sequence of proteolytic activity that is stimulated by a rise in [Ca2+]i. Ca2+ might either trigger protease activity directly or indirectly, or promote the release of lysosomal enzymes. A high [Ca2+]i in dystrophic muscle is believed to be the resultant of a sequence of events that is summarized in the figure. Suggestions are presented for different ways in which the steady-state position of [Ca2+]i might ultimately be controlled for the clinical amelioration of some dystrophic conditions.

Human leucocyte migration inhibitory factor (LIF). V. Specific regulation of the lymphokine serine protease activity by 3',5'-cGMP and, possibly, 2',3'-cCMP

The cyclic nucleotides guanosine 3',5'-cyclic monophosphoric acid (3',5'-cGMP) and cytidine 2',3'-cyclic monophosphoric acid (2',3'-cCMP) but not cyclic phosphodiesters derived from the bases adenine and uracil preserved LIF activity against the blocking effect of the serine protease inhibitor phenylmethylsulphonyl fluoride (PMSF). Phosphomonoesters derived from guanosine and cytidine as well as 2',3'-cGMP and 3',5'-cCMP were all inactive, indicating specificity for phosphodiester bonds and their respective positions in the two active nucleotides. The protection afforded by 3',5'-cGMP and 2',3'-cCMP was dose dependent. Thus, using 10(-3) M PMSF, 3',5'-cGMP was active at concentrations higher than 10(-5) to 10(-4) M, and 2',3'-cCMP at concentrations higher than 3 X 10(-4) to 10(-3) M. The more pronounced LIF-inhibitory effect obtained by increased concentrations of PMSF could be overcome by raising the levels of the nucleotides, indicating that the interactions between PMSF and the nucleotides with LIF were mutally exclusive. The possibility that 3',5'-cGMP and perhaps 2',3'-cCMP function as modulators of LIF is discussed, and models for the function of this lymphokine are proposed.

Prostaglandins, thromboxanes, and polymorphonuclear leukocytes: mediation and modulation of inflammation

When appropriately stimulated (even in the absence of phagocytosis), human polymorphonuclear leukocytes release and/or generate proinflammatory materials and substances capable of provoking tissue injury. These include hydrolases and nonenzymatic substances ordinarily contained within lysosomes, as well as oxygen-derived free radicals. It is now possible to add prostaglandins and thromboxanes to this list. Whereas prostaglandins are capable of eliciting many phenomena associated with inflammation, their effects on cyclic nucleotide metabolism may render these compounds antiinflammatory. Thus, the very cells that release mediators of inflammation provide a mechanism for modulating the inflammatory response.

Pancreatic acinar cell metabolism and function

This review outlines progress made during the past 11 years in research related to pancreatic acinar cell metabolism and function. We have reviewed information gained at the cellular level concerning structural and functional relationships, and effects of fasting and feeding, as well as the action of gastrointestinal hormones and cholinergic agonists on acinar cells. In toto, this information outlines a significant role for gastrointestinal hormones as mediators of secretion, synthesis, and control of trophism. This information provides a basis for more sophisticated inquiries as to the mechanisms of injury of alcohol and drugs. The information may prove helpful in developing diagnostic modalities for pancreatic disease, as well as understanding the processes involved in neoplastic transformation.

Effects of phenytoin on the cyclic nucleotide system in the motor nerve terminal

The effects of phenytoin on the motor nerve terminal were evaluated on the in vivo cat soleus nerve muscle preparation. Phenytoin, 10 mg/kg, reduced the repetitive aftercharges in motor nerve endings due to tetanic conditioning. It also reduced the repetitive activity due to adenylate cyclase activation with NaF, or to exogeneous dibutyryl cyclic AMP. These effects of phenytoin could be reversed by administering theophylline, a phosphodiesterase inhibitor, or by increasing the extracellular concentration of calcium. The effects of phenytoin could also be reversed by 3-aminopyridine, but not by tetraethylammonium chloride. Verapamil, a calcium current antagonist, produced effects that were identical to phenytoin. It is concluded that phenytoin blocks a cyclic nucleotide-mediated calcium influx that is associated with transmitter release. This calcium flux also appears to control a slow potassium current that is responsible for post-tetanic hyperpolarization.

The role of cyclic nucleotides in the CNS

On the basis of the information presented in this review, it is difficult to reach any firm decision regarding the role of cyclic AMP (or cyclic GMP) in synaptic transmission in the brain. While it is clear that cyclic nucleotide levels can be altered by the exposure of neural tissues to various neurotransmitters, it would be premature to claim that these nucleotides are, or are not, essential to the transmission process in the pre-or post-synaptic components of the synapse. In future experiments with cyclic AMP it will be necessary to consider more critically whether the extracellularly applied nucleotide merely provides a source of adenosine and is thus activating an extracellularly located adenosine receptor, or whether it is actually reaching the hypothetical sites at which it might act as a second messenger. The application of cyclic AMP by intrcellular injection techniques should minimize this particular problem, although possibly at the expense of new diffulties. Prio blockade of the adenosine receptor with agents such as theophylline or adenine xylofuranoside may also assist in the categorization of responses to extracellularly applied cyclic AMP as being a result either of activation of the adenosine receptor or of some other mechanism. Utimately, the developement of highly specific inhibitor for adenylate cyclase should provide a firm basis from which to draw conclusions about the role of cyclic AMP in synaptic transmission. Similar considerations apply to the action of cyclic GMP and the role of its synthesizing enzyme, guanylate cyclase. The use of phosphodiesterase inhibitors in studies on cyclic nucleotides must also be approached with caution. The diverse actions of many of these compounds, which include calcium mobilization and block of adenosine uptake, could account for many of the results that have been reported in the literature.