The Effects Of Propofol On Large-Conductance Ca²⁺-Activated K⁺ Channels And Store-Operated Calcium Channels In Rat Arterial Smooth Muscle Cells

BackgroundPropofol is a popular intravenous anesthetic but its use in anesthesia induction and maintenance is frequently associated with haemodynamic alterations such as hypotension. Propofol-induced hypotension may be partly mediated by an inhibition of the sympathetic outflow and impairment of the baroreflex regulatory mechanisms. Reduced vascular tone may also contribute to hypotension following induction with propofol. In vascular endothelial cells, propofol was found to stimulate the production and release of nitric oxide (NO). Propofol can also directly affect arterial smooth muscle tone acting indirectly via the endothelium.Large-conductance Ca2+-activated K+(BKCa) channels and store-operated Ca2+ channels(SOC) are the very important channels in vascular smooth muscle cells, which have mostly intimate relationship with concentration of calcium. Previous pharmacological evidence suggested indirectly that activation of the BKCa channels might account for the vasodilatory effect of propofol.In the first part,to search for the direct evidence we have recorded the current of BKCa channel(IKCa) in arterial smooth muscle cells acutely dissociated from the rat abdominal aorta using the whole-cell voltage-clamp recording technique and the effect of propofol on it.In the second part,the effect of propofol on SOC which is important to the concentration of intracellular Ca2+ in arterial smooth muscle cells has been researched.We approached the mechanisms of propofol-induced vasodilatation to view from the angle of ion channels in vascular smooth muscle cells.Objective1. To assess whether propofol has direct influence on BKCa channels of rat vascular smooth muscle cells.2. To investigate the effect of propofol on SOC by the effects of it on ATP-induced calcium entry and thapsigargin-mediated calcium entry in rat vascular smooth muscle cells. Materials and Methods1. Single rat vascular smooth muscle cell was acutely dissociated from rat aorta. IKCa of smooth muscle cell was recorded by whole-cell patch clamp.IKCa was identified by paxilline which was a specific blocker of BKCa channels.2. The effects of propofol at different concentrations(3×10-5mol/L,1×10-4mol/L,3×10-4mol/L,1×10-3mol/L)on IKCa of rat abdominal aorta smooth muscle cells were observed.3. The IKCa of rat mesenteric aorta smooth muscle cells was recorded by whole-cell patch clamp. The effect of propofol(3×10-4mol/L) on IKCa were observed.4. Rat abdominal aorta smooth muscle cells were loaded with fluorescent indicator. The change of fluorescence intensity represented the change of Ca2+ concentration.The effects of propofol on ATP-induced calcium entry were observed both in the presence of extracellular Ca2+ and in the absence of extracellular Ca2+.5. Rat abdominal aorta smooth muscle cells were loaded with fluorescent indicator. The effect of propofol on thapsigargin-mediated calcium entry was observedResults1. Outward currents were evoked by depolarizing pulses exceeding a threshold of between 20-30 mV above zero,which were consistent with the characteristics of IKCa.The currents which were blocked by paxilline were confirmed to be IKCa.2. The IKCa of rat abdominal aorta smooth muscle cells were inhibited by propofol in a concentration-dependent manner.3. The IKCa of rat mesenteric aorta smooth muscle cells were inhibited by propofol(3×10-4mol/L)4. Propofol(3×10-4mol/L) had a inhibitory effect on ATP-induced Ca2+ rise in rat abdominal aorta smooth muscle cells in the presence of extracellular Ca2+,but not in the absence of extracellular Ca2+.5. Propofol(3×10-4mol/L) had a inhibitory effect on thapsigargin-mediated calcium entry in rat abdominal aorta smooth muscle cells. Conclusions1. Propofol has a inhibitory effect on BKCa channels of rat arterial smooth muscle cells.2. Propofol has a inhibitory effect on SOC of rat arterial smooth muscle cells.