The effects of transition metals on the palatal chemoreceptors of the carp

Abstract

The effects of several heavy metal salts on the carp palatal chemoreceptors were studied by applying the metal salts externally to the taste sensitive area of the palatal organ while recording the electrical responses from the palatine nerve innervating the organ. Treatments of the organ with low concentrations of Na2PtCl6, NaAuBr4, NaAuCl4, HgCl2, and TlCl3 for a short period depressed the response to sucrose. The response to sodium chloride was not affected or occasionally enhanced slightly by these metal salts. CuSO4, ZnSO4, AgNO3, and UO2(CH3COO)2 tended to depress both the responses to sucrose and sodium chloride simultaneously. The gold depression of the sugar receptor increased with rising concentration of NaAuCl4 and was recovered by cysteine. These results suggest that the reaction of the receptor with the chloraurate does take place at the receptor membrane, perhaps at the receptor site. N-ethylmaleimide and iodoacetate depressed non-selectively the responses to sucrose and sodium chloride. Histidine, though more weakly than cysteine, could recover the gold depression of the sugar receptor. These data, along with the non-selective depression by the above metals, suggested participation of some reactive groups other than the sulfhydryls in the reaction of the receptor membrane with gold ions, while some of the above mentioned data suggests an involvement of -SH groups in the reaction of the receptor. This investigation was supported by grants from the Ministry of Education and the United States Public Health Service (2 RO1 NB 04727–04). The author is indebted to the late Dr. J. Konis HI for his support and encouragement. He wishes to thank Dr. M. Ito, Dept. Chem., Mie Pref. Univ., for helpful discussion and criticism. Thanks are also due to Miss F. Higashiura and Mrs. S. Amano for their generous assistance in carrying out the experiments. © 1970, PHYSIOLOGICAL SOCIETY OF JAPAN. All rights reserved.