Effects Of PH₀ On Membrane Potential And K～+ Channels' Activity In Aortic Smooth Muscle Cells

Acid-base balance is an important factor to maintain the homeostasis. The normal pH value of extracellular fluid(pH0) is around 7.35-7.45. Under some physiological or pathological conditions, for example, tissue anoxia, acidosis and alkalosis, pH0 may fluctuate between 6.5 and 8.1, which can induce the changes of vascular tension. These changes are different in different tissues or vessel segments, for example, pulmonary artery contracts but cerebral vessel relaxes during acidosis. However the mechanism hasn't been explained very well yet. Someone reports that pH0 affect the vessels?tension by changing the vascular active substances released by endothelial cells. Others report that pH0 effect the tone by affecting metabolism and signal transmission. And pH0 may act on vascular smooth muscle cells (VSMC) directly to change its tension. This function has close relation with K+ channels in VSMC. At present there are many reports on resistance vessels, for example, pulmonary artery cerebral vessels and mesentery. But the mechanism of how pH0 affecting the tone in large vessels is not known completely. For further researching the ionic mechanism of how pH0 affecting the vascular tone, cell-culture and whole-cell patch clamp technology were used to study the influence of pH0 changes on k+ channels in aortic smooth muscle cells. Methods: 1. SD rat aortic SMCs were cultured through tissue pieces method and identified by inimunohistochemical methods. And calf aortic, pulmonary artery endothelial cells were cultured for studying the effects of vascular heterogeneity on the changes of vessel tension promoted by pH0. 2.The membrane potential and K+ channels of aortic SMCs were record with whole-cell patch clamp: holding potential (Hp) OmV, 1 OmV voltage clamp step, total 13 steps. The special K+ channel blockers was used to identify the types of K+ channels. Whole-cell recording technology was used to research the membrane potential and membrane current of RFI6A. 3. The effects of pH0's acute and chronic changes on K+ channels? activities in aortic SMCs were studied with whole-cell recording technology. (1) acute changes: Cells were exposed to extracellular fluid of pH7.2→pH6.5→pH7.2 in turn, or pH7.2→pH8.1→pH7.2. (2) chronic changes: Cells were incubated with 8.8% C02,for 8d,then the potential was recorded. In other experiments, extracellular fluid containing TEA (5mM) or 4-AP (5mM)was used to study the changes of the currents to make sure the evolved channels?type. Result: 1. Successful culture and identification of the aortic SMC, calf aortic and pulmonary artery endothelial cells and brain capillary endothelial cells. 2.The resting potential of aortic SMC is -37±5mV (n=30). K+0 is the main K+ channel of the SMC and sensitive to TEA (5mM) but insensitive to 4-AP (5mM). Ach has no effects on this channel. There is a bimodal distribution of resting potentials with peaks around -25mV and -55mV. There are three kinds of K+ channels: Ca-activated K+ channel (KCa), transient-outward K+ channel (Kt), and inward- rectified K+ channel (KIR). 3 .During the acute changes of pH0, the decreasing of pH0 heperpolarized the membrane potential and increased the K+ current. On the other hand the pH0 increase depolarized the membrane potential and decreased the K4 current. TEA can block this change...