An improved microrespirometer for tissue slices

Abstract

The differential capillary respirometer consists essentially of two chambers, one of which contains a tissue slice, joined by a horizontal capillary. The capillary contains a droplet of fluid which moves if gas is absorbed or evolved in one of the chambers. Compared with open-ended (Warburg) respirometers, this arrangement is free from interference clue to changes in the barometric pressure or environmental temperature. The sensitivity of the differential capillary respirometer depends only on the diameter of the capillary and is not affected by the size of the chambers. The speed of response is inversely related to the chamber volume, however, so the chambers should be as small as possible. The earliest instruments were constructed of glass by Thunberg (1) and developed further by Fenn (2, 3). The Fenn respirometer had the advantages of all-glass construction, i.e., ease of cleaning, visibility of the chamber contents, and rapidity of assembly by ground-glass joints. Disadvantages included the USC of a curved capillary which may interfere with the movement of indicator fluid and the use of side arms for additions during incubation. This latter feature set. a lower limit to the size of the chambers and therefore also to the rapidity of response. In 1940, Cunningham and Kirk (4) described an instrument with the chambers formed from cavities drilled in two metal blocks. This design has been modified in various ways (5-9). Respirometers of metal block construction have the advantage of easier temperature equalization bctween the two chambers and of easier construction of equal chamber size. They may also be made very compact although this requires the use of curved capillaries. These advantages are offset by some serious disadvantages, The instruments are cumbersome to assemble, the chamber