Research for oxygen sensitive ionic channels of vascular smooth muscle cells

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We had explored the O_2 sensitive ion channels of vascular smooth muscle (VSM) cells using whole-cell voltage clamp. We found the following results in two years (2000-2001).1. To investigate the role of Na-Ca exchange in the hypoxia induced vasoconstriction, we evaluated the developmental changes of Na-Ca exchange current of the resistance pulmonary artery (PA). Conclusions : The Na-Ca exchanger is present in both the premature and mature resistance PA. Hypoxia attenuates the Na-Ca exchange inward current in the mature resistance PA VSM cells. In the premature resistance PA, the increased activity to extrude cytoplasmic Ca via Na-Ca exchange may function to compensate for the hypoxia induced [Ca]i rise.2. The contraction of ductus arteriosus (DA) does not often occur in premature new born (NB). As an O_2 sensor of DA, O_2 sensitive K_V and K_<ATP> have been implicated and these ion channels may be underdeveloped in premature NB. The purpose of the present study was to investigate development of these ion channels in the DA VSM cells. Conclusions : In the DA, both O_2 sensitive K_V and K_<ATP> are underdeveloped in the premature fetus. In addition to O_2 sensitive K_V, K_<ATP> may also be important as an O_2 sensor in the DA.3. Under hypoxic conditions, O_2 sensitive K_V may be closed, resulting in PA vasoconstriction and K_<ATP> may be activated, preventing excessive vasoconstriction. The purpose of the present study was to investigate developmental changes of K_<ATP> in the resistance PA VSM cells. Conclusions : In NB, KATP is present in the small resistance PA and it decreases with development. Since the currents in the small PA with membrane potential between -60 to 0 mV are small, the role of K_<ATP> may not be important under physiological conditions, but may be important for vasodilation during the perinatal hypoxic conditions in NB.