Measurement of hydraulic conductivity in single perfused microvessels has been carried out over the last thirty years using the Landis-Michel technique or modifications of it (Michel et al. 1974). These involve cannulation and perfusion of a microvessel in a thin tissue such as the mesentery with physiological solutions containing red blood cells as flow markers. The rate of filtration or absorption to or from the tissue is measured by movement of the red cells during occlusion by a fine glass rod. These techniques have ably demonstrated the relationship between pressure and filtration rate (Starling, 1896). They have also enabled measurements of oncotic reflection coefficients to molecules such as albumin. The use of this technique has previously described transient absorption when perfusing with small molecular weight substances such as glucose and sodium ions that exert a transient osmotic pressure across the vascular wall (Curry et al. 1976). Here we demonstrate an unusual osmotic transient caused by perfusing dimethyl sulphoxide (DMSO), a compound often used as a solvent for hydrophobic compounds, particularly pharmacological agents. Frogs anaesthetised by immersion in 1 mg ml-1 MS222 and kept anaesthetised by superfusion of 0.25 mg ml-1 MS222 in frog Ringer solution were prepared for Lp measurement as described extensively in the literature (Bates & Curry, 1996). At the end of the experiment frogs were killed by cranial destruction. The vessels were cannulated and perfused with 1 % BSA in frog Ringer solution and Lp measured by occlusion. The pipette was then refilled with 0.5 % DMSO in 1 % BSA frog Ringer solution using a previously described syringe refiller (Hillman et al. 2001). Filtration rate was then measured by occlusion. Immediately upon occlusion of the vessel during perfusion with 0.5 % DMSO a transient, decreasing absorption was seen which reversed within 1-2 min to filtration. After the occlusion was lifted flow resumed again as usual. Upon repeat of the occlusion a similar transient absorption was again measured, and this occurred for all subsequent occlusions. We speculate that this transient absorption is an osmotic transient caused by local changes in salt concentration elicited by the effect of DMSO on the cell membrane.
This work was supported by the British Heart Foundation (FS2000057 and FS98023).
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