The long-term objectives of the proposed study are to elucidate the mechanisms whereby various therapeutic drugs exert their effects on neuroreceptor/channel systems. Emphasis is placed on their actions on voltage-activated channels and transmitter receptor-channel complexes. Patch clamp techniques will be used to record whole cell and single channel currents. Several classes of drugs and chemicals will be studied. Opioids have been demonstrated to block certain types of voltage-activated calcium channels through their action on opioid receptors. Agonist-receptor-calcium channel relationship, which has been controversial somewhat, will be established using different opioids and different preparations which include mouse neuroblastoma-glioma hybrid cells (NG108-15), human neuroblastoma cells (SH-SY5Y), and rat dorsal root ganglion neurons. Available evidence suggests that G proteins and/or second messengers are involved in the action of opioids. This problem will be studies by combining appropriate inhibitors such as pertussis toxin and staurosporine with calcium channel current recording. Calcium channel currents have been found to exhibit a gradual decrease and a large increase (rebound) during and after application of opioid, respectively. These mimic tolerance and withdrawal symptoms. Single channel analyses will be performed to elucidate the mechanisms underlying these phenomena. The excitatory amino acid (EAA) receptor-channel system is an important site of action of various therapeutic agents. Patch clamp analyses will be performed to elucidate the mechanism of action of certain antidepressants, psychotropic drugs, polyamines, and polyvalent cations on EAA-induced currents. These drugs include imipramine, desmethylimipramine, haloperidol, barbiturates and chlorpromazine. Attention will be focused on their mode of interactions with channel currents at both whole cell and single channel levels, their sites of action on the receptor-channel complex, and the interactions between these drugs and polyvalent cations. Some divalent cations such as Mg2+ and Zn2+ have been studied extensively and are useful as tolls for the study of drug action. Polyamines such as spermine, spermidine and putrescine have been suggested to modulate the EAA system and will be subjected to single channel analyses. These are tetrodotoxin (TTX)- resistant sodium channels in rat dorsal root ganglion neurons. Their physiological and pharmacological properties have been found to be considerably different from those of TTX-sensitive sodium channels. Whole cell and single channel analyses will be conducted to characterize then in comparison with TTX-sensitive channels. These differences are of particular importance from the pharmacological point of view as various therapeutic drugs are known to act on sodium channels.
Showing the most recent 10 out of 65 publications
