Effects of normo- and hyperbaric pressure on an acetylcholine-binding proteoglycolipid from rat gastrocnemius tissue

Electrophysiological studies on the effects of opiates on dorsal horn nociceptive neurones at 51 atmospheres absolute

The purpose of this study was to investigate the effects, if any, of high pressure on opiate analgesia. The interaction of high pressure with intrathecal morphine (2.5-15 micrograms) and pethidine (10-145 micrograms) was studied on the responses of 51 dorsal horn neurones in the intact rat under urethane anaesthesia to electrical stimulation applied to their receptive fields. Two types of response to the addition of the opiates were found. Cells were either rapidly and maximally inhibited by the lowest dose of morphine (2.5 micrograms) or pethidine (10 micrograms) or slowly inhibited in a dose-dependent manner with an ED50 of 13.6 nmol for morphine and 401 nmol for pethidine. Pressure did not significantly affect the time-response curves for these two types of response but did change the relative numbers of each type recorded. The number of cells totally inhibited by the lowest of drug concentrations was increased for morphine at pressure but decreased for pethidine.

The effects of pressure on the molecular structure and physiological functions of cell membranes

The effects of high pressure on the phase state and molecular structure of pure lipid bilayers are discussed. The relations of delta H, delta S and delta V in phase transitions are straightforward and are discernible in heterogeneous bilayers in natural membranes. The effects of pressure on the dynamic properties of bilayer constituents are less clearly understood, but order parameters obtained at pressure by different techniques show agreement. The extent and significance of hydration is poorly understood. Four physiological functions are discussed: passive permeability, active transport, membrane excitability and synaptic transmission. It is shown that a full interpretation of the kinetic effects of pressure on these processes requires much more detailed molecular information than is available at present.