Blockade of the ATP-sensitive potassium channel by taurine in rabbit ventricular myocytes

Using patch-clamp techniques, the effects of taurine on properties of ATP-sensitive K+ (KATP) channel of rabbit ventricular myocytes were examined. Intracellular taurine (20 mM) markedly depressed the KATP channel activity. The taurine concentration for half-inhibition (apparent Kd) was 13.5 mM with a Hill coefficient, n, of 1.3. Intracellular taurine caused channel inhibition without affecting channel inhibition by ATP. In control conditions, the ATP concentration for half-inhibition (Ki) and n were 73 microM and 1.2 (n = 6), respectively. In the presence of taurine, Ki and n were 81 microM and 1.3 (n = 6), respectively. Analysis of the open and closed time distributions showed that taurine decreased the life time of bursts and increased the inter-burst interval and/or reduced the number of functional channels. 2,4-Dinitrophenol (DNP) activated KATP channel after a lag period. This lag period was much longer after pretreatment with taurine (6.6 +/- 1.2 min, n = 5) than in the absence of taurine (2.8 +/- 1.5 min, n = 12). When DNP was removed in the bath solution, channel activity showed a gradual reduction with time and this process was facilitated by the presence of external taurine (20 mM). From these results it is suggested that taurine blocks KATP channel activity in dose-dependent manner and the depletion of taurine during myocardial ischemia contribute to the early activation of the KATP channel.