Microiontophoretic release of drugs from micropipettes: use of 24Na as a model.

1. The use of (24)Na(+) of high specific activity allowed its iontophoretic release from multibarrelled glass micropipettes to be followed over short periods with low currents.2. When a negative retaining current was passed to reduce diffusional efflux between the periods of positive current expulsion of (24)Na(+), the rate of release of (24)Na(+) during the expulsion period progressively increased during the first minute before becoming constant.3. The currents employed were similar to those normally used to regulate the microiontophoretic release of potent drugs such as gamma-aminobutyric acid. It is therefore concluded that, during the usual period of response to such drugs, the rate of release of drug is not constant but increasing.4. The implications of these observations for the construction of microiontophoretic dose-response relationships is discussed.