Electrophysiological responses of crayfish oocytes to biogenic amines

Intracellular recordings were made from immature, growing oocytes of the cr ayfish Pacifastacus leniusciulus. Oocytes had a relatively negative resting potential of - 74.7 +/- 2.2 mV (n = 26; range - 53 to - 90) and a mean inp ut resistance of 0.86 +/- 0.19 M Omega (n = 22; range 0.17-3.3). Octopamine induced a long-lasting response involving biphasic changes in input resist ance, together with bi- or multiphasic changes in membrane potential. The r esistance-decreasing phase involved tin different oocytes) membrane hyperpo larization, depolarization or both. The resistance-increasing phase was usu ally a depolarization. The hyperpolarizing form of the resistance-decreasin g response, and the depolarizing resistance-increasing response reversed in polarity at membrane potentials of(respectively) - 90 and - 92 mV, suggest ing increases and decreases in K+ conductance underly the biphasic changes in input resistance. The threshold concentration for the response was remar kably low (>10(-12) M) and showed little or no dose-dependence over the con centration range 10(-12)-10(-6) M. Similar responses were evoked by dopamin e and serotonin (at 10(-9) M), although a higher proportion of oocytes resp onded to octopamine and/or dopamine than to serotonin. (C) 2000 Elsevier Sc ience Inc. All rights reserved.