Synaptic transmission at high pressure: Effects of [Ca²⁺]_o

1. 1. The effects of pressure on synaptic currents were examined in crayfish abdominal muscles. 2. 2. Helium pressure (10.1 MPa) considerably decreased extracellulariy-recorded excitatory junctional potentials associated with increased short-term facilitation. 3. 3. These effects could be mimicked by a reduction of [Ca²⁺]_o, and partially compensated by an increase in [Ca²⁺]_o. 4. 4. Pressure also reduced the amplitude of the extracellular nerve terminal potentials (ENTP) by up to 25%, and significantly increased synaptic delay in a [Ca²⁺]_o-dependent manner. 5. 5. The interaction between compression and various [Ca²⁺]_o were analysed in terms of an existing model of transmitter release. The results were consistent with the hypothesis that high pressure decreases the maximal Ca²⁺ influx into nerve terminals. 6. 6. The decreased ENTP and increased synaptic delay suggest that additional processes may be involved in pressure effects on synaptic transmission.