TY - JOUR T1 - INTERFERENCE WITH EXCITATION BY 5-BENZOYLOXY-2-IMINOHEXAHYDROPYRIMIDINE HYDROCHLORIDE JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 34 LP - 39 VL - 177 IS - 1 AU - M. Y. SPIEGELSTEIN AU - C. Y. KAO Y1 - 1971/04/01 UR - http://jpet.aspetjournals.org/content/177/1/34.abstract N2 - This substance (to be coded as HM-197) is a new synthetic guanidinium ester possessing some similarity to a partial structure of tetrodotoxin. Studies of its actions on the electrical properties of the isolated frog sartorius muscle were made, using intracellular constant current polarization and intracellular recording. Significant depolarization occurred in concentrations lower than 100 µg of HM-197 per ml, but not in concentrations higher than 200 µg/ml. The higher concentrations also reversed depolarizations produced by prior doses of lower concentrations. With higher and nondepolarizing concentrations, the spike threshold was significantly increased (from -58 to -45 mV) and the spike amplitude was significantly reduced (from 112 to ca. 90 mV). The compound did not alter the effective resistance or the current-voltage relation for inward or outward currents, suggesting that it did not affect the chloride and potassium conductances and only affected the spike generating mechanism in a manner similar to that of tetrodotoxin. HM-197 is not an antagonist but may be a partial agonist of tetrodotoxin and saxitoxin. © 1971, by The Williams & Wilkins Company ER -