The resting potential of cockroach muscle membrane

1. 1. Evidence is presented that E m of cockroach muscle has two components, an active component generating about 18 mV and an ionic electrode, dominated by K +, which is responsible for about 42 mV. 2. 2. Equilibration between the saline and extracellular fluid is probably complete within 60 min. 3. 3. E m vs. log [K +] o produces a linear plot with a slope of 43 mV for a 10-fold change in [K +] o. 4. 4. E m> E K. 5. 5. The active, electrogenic component is inhibited by metabolic inhibitors, low temperature, anoxia, ouabain, absence of [HCO 3 −] o and omission of [Cl −] o. The nature of this component is discussed and it is believed that one of its functions is the outward transport of K +. 6. 6. The role of [Cl −] o is discussed. 7. 7. When metabolism is inhibited the membrane depolarizes and E m becomes insensitive to reductions in [K +] o, an effect which disappears in the absence of [Na +] o. Under these conditions, P K outwards is believed to be very low. 8. 8. Comparisons are made with results obtained with other insects and similarities with mammalian smooth muscle are emphasized.