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

Abstract

1 The use of ²⁴Na⁺ 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 ²⁴Na⁺, the rate of release of ²⁴Na⁺ 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 γ-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.