Comparative electrophysiology and pharmacology of mammalian (including one marsupial) intercostal muscle biopsy preparations.

Characteristics of minature end-plate potentials (MEPP) of isolated external intercostal muscle preparations of 7 mammalian species (dog, cat, pig, horse, cow, and goat) including 1 marsupial (opossum, Didelphis marsupialis) were determined with intracellular microelectrodes. Mean amplitude (+/- standard error of MEPP for all species was 0.60 +/- 0.06 mV, and the range was 0.28 mV (opossum) to 1.07 mV (pig). Amplitude was inversely correlated (P less than 0.01) with muscle fiber diameter which ranged from 93 mum (opossum) to 51 mum (pig). Mean values for rise time, half-decay time, and frequency of MEPP for all species were 0.88 +/- 0.07 msec, 1.89 +/- 0.16 msec, and 0.44 +/- 0.12 MEPP/second, respectively. Species differences among these measurements were not statistically significant. Resting potentials ranged from 64 mV (pig) to 75 mV (cow and opossum). Amplitude of MEPP was reduced significantly by d-turbocurarine (0.06 muM) only in preparations from the dog (P less than 0.01), pig (P less than 0.05), cow (P less than 0.01), and goat (P less than 0.01), suggesting species variations in sensitivity to this neuromuscular blocking agent. Frequency of MEPP decreased in the prescence of d-tubocurarine, but the change was not significant. The techniques utilized in this study and the results obtained will have application in evaluation of intercostal muscle biopsy preparations from these species when affected by myasthenic diseases.