Temperature-controlled perfusion apparatus for microscope using transparent conducting film heater

We describe a novel temperature-controlled perfusion apparatus for electrophysiological studies on isolated cells or membrane patches. The apparatus uses a transparent conducting film of indium-tin-oxide as a heating element. The film heater deposited on a glass sheet allows us to construct a structurally simple apparatus that is able not only to heat directly the bath chamber but also to preheat the perfusion solution on the stage of an inverted microscope. The structure ensures a uniform temperature in a bath chamber that has a working area of approximately 6 X 12 mm2 and a capacity of 1 ml. A control unit, designed for operation of the apparatus, regulates the temperature of the bathing solution without introducing electrical noise in a range from ambient temperature to greater than 37 degrees C with an accuracy within +/- 1 degree C. The apparatus is 12 mm in height and designed to fit on the stage of a standard inverted microscope. Since the bath chamber for perfusion experiments is readily interchanged with others, the apparatus can be used widely in microscopic studies of various cells in static solutions.