Figure 1.
Comparison of the potency of diazoxide and pinacidil in activation of KATP membrane currents at −50 mV in pig urethra. Nystatin-perforated patch configuration; the bath contained a 140 mM K+ solution and pipette 140 mM KCl containing 5 mM EGTA (i.e., symmetrical 140 mM K+ conditions). (a) Diazoxide (100 – 500 μM) caused an inward membrane current in a concentration-dependent manner. On removal of diazoxide, the current recovered to the control level. Subsequent application of pinacidil (100 μM) caused an inward current. The dashed line indicates zero current level. (b) The relation between the concentrations of KATP channel openers and the relative peak amplitude of KATP channel opener-induced membrane currents in pig urethra. Note that the peak current amplitude was measured from the level before application of KATP channel openers and normalized with respect to the 100 μM pinacidil-induced current from the same dispersed myocytes. The following values were used for the curve fitting: A=1.1, K=15 μM, nH=1.2. The line for the diazoxide-induced current was drawn by eye. Each symbol indicates the mean of 3–10 observations with ±s.d. shown by vertical lines. (c) Diazoxide (500 μM) enhanced the 10 μM pinacidil-induced current. The dashed line indicates zero current level. (d) The effects of diazoxide and pinacidil were additive. The different symbols represent four separated experiments. The arrow between points indicates the order of application of the KATP channel openers (diazoxide and pinacidil) onto the same dispersed cell. Asterisks indicate a statistically significant difference, demonstrated using a paired t-test (P<0.05).