EFFECT OF CHRONIC HYPOXIA ON K- REGULATION IN HUMAN PULMONARY VASCULAR SMOOTH-MUSCLE CELLS( CHANNELS )

We investigated the effects of chronic hypoxia on the major outward K currents in early cultured human main pulmonary arterial smooth muscl e cells (HPSMC). Unitary currents were measured from inside-out, outsi de-out, and cell-attached patches of HPSMC. Chronic hypoxia depolarize d resting membrane potential (E-m) and reduced the activity of a chary bdotoxin (CTX)- and iberiotoxin-sensitive, Ca2+-dependent K+ channel ( K-Ca). The 4-aminopyridine-sensitive and CTX-insensitive channel or th e delayed rectifier K+ channel was unaffected by chronic hypoxia. Chro nic hypoxia caused a +33- to +53-mV right shift in voltage-dependent a ctivation of K-Ca and a decrease in K-Ca activity at all cytosolic Ca2 + concentrations ([Ca2+](i)) in the range of 0.1-10 mu M. Thus the hyp oxia-induced decrease in K-Ca activity was most likely due to a decrea se in K-Ca sensitivity to E-m and [Ca2+](i). Chronic hypoxia reduced t he ability of nitric oxide (NO .) and guanosine 3',5'-cyclic monophosp hate (cGMP) to activate K-Ca. The cGMP-dependent protein kinase-induce d activation of K-Ca was also significantly inhibited by chronic hypox ia. In addition, inhibiting channel dephosphorylation with calyculin A caused significantly less increase in K-Ca activity in membrane patch es excised from chronically hypoxic HPSMC compared with normoxic contr ols. This suggests that the mechanism by which hypoxia modulates NO .- induced K-Ca activation is by decreasing the NO ./cGMP-mediated phosph orylation of the channel.