Effects Of Propofol On L-type Calcium Channel Of Guinea-pig Smooth Muscle

Objective:To study effects of propofol on L-type calcium channel of guinea-pig smooth muscle. Further to investigate effects of propofol on gastrointestinal motility.Methods:We used traditional whole-cell patch clamp technique to record the L-type calcium current (ICa2+) under Ca2+-PSS superfusion, then substituted Ca2+ with Ba2+,and recorded IBa2+.10% fat milk was used as control. Changes of IBa2+ were observed when cells were superfused with fat milk.Normal cells were also superfused with different concentrations of propofol (2μg/ml and 78μg/ml), changes of IBa2+ were recorded when cells were stimulated by single pulses. We needed more than three sets of data in each group.Results:Cells are superfused with Ca2+-PSS. Under whole-cell configuration, membrane potential was clamped at-80mV, and ICa2+ was elicited by step voltage command pulse from -60 to +60 mV for 400 ms with 10 mV increments at 10s intervals. ICa2+ started to show up at -30 to-20mV,and reached peak value of (-63.62±19.46) pA at 0mV,and the reversal potential was about +40mV. After Ca2+ was substituted by Ba2+, IBa2+ showed the same feature as ICa2+,but the peak value of IBa2+ increased to(-286.63±51.57) pA. The fat milk superfusion did not affect IBa2+.Then membrane potential was clamped at -80 mV, and IBa2+ was elicited by a single step command pulse from -80 to 0 mV for 400 ms at 10 s intervals. The time-course showed that when 2μg/ml propofol was added (n=4),IBa2+ increased slightly for about 30s, and then decreased gradually. 170s later, IBa2+ was steady and achieved (66.32±4.41)% of the normal current.IBa2+ restored to (91.83±1.24)% of normal current after washing. When cells were superfused with 78μg/ml propofol (n=3), IBa2+ decreased gradually and achieved (75.63±3.51)% of the normal current after 190s and restored to (94.58±3.19)% of normal current after washing.Conclusion:According to the results of whole-cell patch clamp technique, we may conclude that subhypnotic dose of propofol inhibited L-type calcium current of guinea pig smooth muscle. That may weaken smooth muscle contraction and may be one of the reasons why propofol inhibited gastrointestinal motility.