An Abstract of the Thesis of Title: a Corntarative Investiaation of the Pharmacoloav of Fish and Mammalian Neuromuscular Systems

approved:_ __ Lavern J. Weber Neuromuscular pharmacology has been extensively studied in mammals but there have been few investigations examining the neuromuscular systems of fish. In situ experiments have shown that the basic cholinergic characteristics of fish neuromuscular junctions are different from those of mammals. In order to further understand the nature of these differences, the riicotinic acetyicholine receptors (AChR) of rat and buffalo sculpin (Enophrys bison) neuromuscular junctions and the AChR of electric ray (Torpedo california) electroplax, were investigated using receptor binding analysis. A rapid filtration assay was utilized to measure [1251]-a-BGT binding to tissue membranes. Scatchard analysis of [125I]--BGT binding was performed on sculpin pectoral muscle, rat gastrocnemius, Redacted for privacy rat denervated gastrocnemius, and Torpedo electroplax. The affinity constant was similar for all tissues studied (KD = 1-5 nIl). The maximal number of binding sites for each tissue (pmole/g tissue) is : Torpedo electroplax = 190; sculpin pectoral = 2.07; rat innervated gastrocnernius = 0.04; rat denervated gastrocnemius = 0.50. Kinetic analysis produced association rate constants for sculpin pectoral muscle: 3.96 x l0 min nrnole; rat dennervated gastrocnernius: 648 x 10 min nmole, and Torpedo electroplax: 4.78 x 108 rniri1 mole1. Dissociation was biphasic in sculpin pectoral with fast and slow dissociating component9', whereas only a very slow dissociating component was detected in Torpedo electroplax and denervated rat gastrocnemius. In competition studies, d-tubocurarine had the highest affinity for the [1251)-a.-BGT binding site in all tissues, illustrating the nicotinic nature of the binding sites. Acetyicholine had high affinity for the rat gastrocnemius binding site and low affinity for the sculpin pectoral muscle and Torpedo electroplax binding site. Atropirie had high affinity for the sculpin pectoral muscle binding site when compared to the rat gastrocnernius and Torpedo electroplax binding site, indicating that the sculpin pectoral site may have some mixed muscarinic-nicitinic characteristics. These results indicate that there are definite qualitative as well as quantitative differences between the fish skeletal muscle nicotinic receptor and the nicotinic receptor of fish electroplax and rat skeletal