Simultaneous analyses of Ca exchange and mechanical parameters in the rat atria.

In the rat left atrium, electrically driven, a superfusion dropping method was developed. The device essentially consisted of a pair of platinum wire electrodes which held one end of the tissue, while the other end was attached to an isometric tension transducer. Either normal or isotopically labeled solutions were poured on the preparation at preset flow rates by means of a minipump. Effluent was collected fractionally in vials for measurement of radioactivity. Several perfusion flows tested led us to the conclusion that higher rates than 2.26 ml/min did not improve contractile performance. Stability of the preparation was found similar to the classical isolated organ-bath method during a 180 min period of observation. Set-up of the superfused atria reproduced paired determinations of 45Ca efflux, together with the contractile parameters. In addition, the frequency of sampling (intervals of 1 min or less) allowed us to detect changes in the washout pattern of exchangeable 45Ca even during early phases of Ca efflux. Therefore, the method reported herein seems to overcome the serious handicap of the scanty tissue employed.