A superfusion bath for single-cell recording with high-precision optical depth control, temperature regulation, and rapid solution switching.
A superfusion system for isolated cell recording, which uses a novel optical technique for feedback control of solution depth (+/- 5 microns), is described. A retroreflective optosensor senses the distance between itself and a white hydrophobic plastic float, supported by surface tension on the surface of the solution. The combination of optical depth sensing with stepper-motor-driven pumps, pneumatic ("noise-free") solution switching and Peltier-effect solution heating/cooling provides a high degree of control over the cell superfusion environment. The solution flow rate to the bath is selected over the range 0.08-5.00 (+/- 0.01) ml min-1 with provision for solution recirculation. The temperature control range of the Peltier element is 4.0 degrees-70.0 degrees C. At temperatures selected over the range 16.0 degrees-36.0 degrees C, and at flow 3.00 ml min-1 the temperature gradient through the central working position of the bath is not more than 0.2 degrees C. At this flow, bath solution exchange on valve actuation is 90% complete within 0.7 s. This superfusion system is particularly suited to conventional and fluorescence imaging techniques where accurate control of the solution level ensures constant optical conditions. In electrophysiological experiments this apparatus will also provide stabilization of electrode capacitance with adjustment of solution depth. The robust and compact design of the system allows it to be carried between different applications.