A variety of agents, including receptor agonists/antagonists and synthetic and natural products, modulate ion channels and generation of second messengers, including cyclic nucleotides, inositol phosphates, diacylglycerides, arachidonic acid, prostaglandins, sphingosine, and phosphatidic acid. Calcium, sodium and potassium ions after translocation through ion channels or by transport proteins can activate or inhibit release and transport processes, contractile proteins, cyclases, phosphodiesterases, protein kinases, phospholipases and ATPases. Modulatory interactions or cross-talk occurs both between the second messenger systems and the ion transport systems. The research of the past year concerned capacitative calcium entry through store-operated calcium (SOC) channels, effects of caffeine and analogs on GABA(A) receptor-channels and ryanodine-sensitive calcium-release channels, and effects of various synthetic and natural products on sodium, potassium and nicotinic channels and muscarinic receptors. Loperamide, a potent blocker of maitotoxin-activated channels, selectively enhances elevation of intracellular calcium linked to influx of calcium through SOC channels, while having no effect on basal levels of calcium. Loperamide reduces the efficacy of SOC channel blockers. Syntheses of analogs of loperamide to probe structure activity relationships are planned. A variety of evidence on activation, blockade and temperature-dependency suggests that there are subclasses of SOC channels even within a single cell type. Imidazoles, such as SKF96365, clotrimazole and miconazole, were found to cause both release of calcium from IP(3)-sensitive pools and blockade of the SOC channels that open as the result of such release. Quaternary imidazoles, such as calmidazolium, caused release of calcium, but did not block SOC channels. Thus, structure activity relationships are not the same for release from od calcium and for blockade of SOC channels. Phenothiazines, such as trifluoperazine, and other tricyclics were found to cause little release and to be effective blockers of SOC channels. Certain dihydropyridines also were effective blockers of SOC channels and caused little release of calcium. Sphingosine and metabolically stable dimethylsphingosine caused a slow, sustained influx of calcium into a human leukemia cell line. An initial release of intracellular occurred with sphingosine dihydrosphingosine and appeared dependent on conversion to sphingosine phosphates. Caffeine and analogs were found to inhibit binding of ligands to both benzodiazepine- and picrotoxinin-sites on GABA(A) receptor-channels. Effects on ion flux will be studied. Caffeine and analogs were discovered to have both stimulatory and inhibitory effects on binding of ryanodine to calcium-sensitive release channels. Certain analogs caused only inhibition, while others caused mainly stimulation. Effects on release of calcium from ryanodine-sensitive storage sites will be investigated. Caffeine inhibits G2 checkpoint, thereby preventing DNA repair in cancer cells lacking P53 function. In a series of 56 caffeine analogs only analogs with alterations at the 1-position retained the inhibitory activity. Further caffeine analogs with altered 1-substituents will be synthesized and probed as adjuvants to cancer chemotherapy. Synthetic analogs of the alkaloid epibatidine are being investigated as selective agonists at nicotinic receptors and have provided further insights into the agonist recognition site of nicotinic receptors. Some of these are related in structure to ABT 594, a synthetic analog of epibatidine, that has completed clinical trials as an analgetic for treatment of chronic pain. Synthetic beta-6-acyloxytropanes were synthesized and shown to be potent agonists for subclasses of muscarinic receptors. Behavioral effects, including analgesia, will be probed with nicotinic and muscarinic agonists. A variety of alkaloids were studied as noncompetitive blockers of the major nicotinic receptor-channels, but all were nonselective or selective for the ganglionic class. Blockade of analgetic effects of epibatidine by such alkaloids will be investigated. Investigation of structure activity relationships of the myotonic/cardiotonic alkaloids of the pumiliotoxin class at sodium and calcium channels are in progress based on sodium flux, calcium release and direct and indirect effects on batrachotoxin binding. There is markedly different structure activity relationships for activation of sodium flux as compared to blockade. Synthetic efforts to develop a relatively non-toxic pumiliotoxin as a cardiac stimulant are in progress. Reserpine and local anesthetics were discovered to have effects on the binding of brevetoxin to sodium channels. Both direct and allosteric effects occurred. Analogs of tetraethylammonium containing from one to four propargyl groups provided insights into the structure of the external pore of potassium channels. The effects of aryl fluorine substition of adrenergic activity of the R- and S- enantiomers of norepinephrine and epinephrine were determined. 2-Fluoro substition militated against proper interaction the R-isomer at lpha-receptors and enhanced interaction at the beta-receptors, while 6-fluoro substition militated against proper docking of the R-isomer at beta-receptors.
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