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 m ) markedly depressed the KATPchannel activity. The taurine concentration for half-inhibition (apparent Kd) was 13.5 m 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 73μ and 1.2 (n=6), respectively. In the presence of taurine, Kiand n were 81μ 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 KATPchannel 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 m ). From these results it is suggested that taurine blocks KATPchannel activity in dose-dependent manner and the depletion of taurine during myocardial ischemia contribute to the early activation of the KATPchannel.