Response to 5-Hydroxytryptamine and Electrophysiology of the Malpighian Tubule Muscle of the American Cockroach, Periplaneta americana1, 2

Abstract

The malpighian tubule muscle of Periplaneta americana (L.) appears to be electrically inexcitable. Small voltage fluctuations with magnitudes less than 1 mv were observed; potentials of larger size did not occur. A transmembrane potential across the muscle of −23.6±1.4 mv (95% C.I.) was recorded; the inside was negative with respect to the outside. In 1.0×10−6 M 5-hydroxytryptamine (5-HT) the transmembrane potential was −20.3±1.0 mv. This 15.3% decrease of the transmembrane potential is suggested to be significant in accounting for the accelerated contraction rate of the tubules caused by 5-HT.