Abstract
1. Membrane slope resistance of Aplysia statocyst receptor cells was measured by passing constant current pulses, using a bridge circuit. In response to downward tilt all cells which responded exhibited depolarization but this could be accompanied by either decrease, increase or no measurable change in slope resistance, depending on resting membrane potential. 2. By altering membrane potential with d.c. and measuring slope resistance with constant current pulses, these cells are shown to exhibit both anomalous and delayed rectification. Either hyperpolarization or depolarization from one potential can cause the slope resistance to decrease by as much as a factor of 5. 3. The response to standard tilt can be changed from an increase in slope resistance to a decrease, or vice versa, by altering membrane potential. 4. When membrane potential was held constant during downward tilt, the slope resistance always decreased. 5. Slope resistance, the voltage response to standard tilts and the amplitude of membrane potential fluctuations all vary with average membrane potential in a similar manner. 6. These findings are incorporated into a circuit model in which anomalous and delayed rectification are represented by voltage-controlled elements. the response to tilt is always modelled as introducing a parallel conductance pathway with a large positive reversal potential. 7. The model demonstrates that slope resistance can be increased by adding a parallel shunt pathway if the latter brings the membrane out of the anomalous rectification region. 8. The model also demonstrates how delayed rectification can greatly alter the reversal potential inferred from measurements at potentials below actual reversal.
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Selected References
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