DIFFERENTIAL OXYGEN SENSITIVITY OF CALCIUM CHANNELS IN RABBIT SMOOTH-MUSCLE CELLS OF CONDUIT AND RESISTANCE PULMONARY-ARTERIES

1. Calcium currents were recorded from smooth muscle cells dispersed f rom conduit and resistance rabbit pulmonary arteries. me tested the hy pothesis that Ca2+ channel activity was regulated by environmental O-2 tension. 2. Conduit (proximal) and resistance (distal) myocytes diffe r in their Ca2+ channel density and responses to low P-O2. Ca2+ curren t density in distal myocytes (20.7 +/- 7.4 pA pF(-1) n = 10) is almost twice the value in proximal myocytes (12.6 +/- 5.5 pA pF(-1), n = 39) . In proximal myocytes, the predominant response to reductions in P-O2 is inhibition of the calcium current (n = 12) at membrane potentials below 0 mV, whereas potentiation of current amplitude is observed in d istal myocytes (n = 24). 3. Hypoxia also produces opposite shifts in t he conductance-voltage relationships along the voltage asis. The avera ge displacements induced by low P-O2 are + 5.05 +/- 2.98 mV (n = 5) in proximal myocytes and - 6.06 +/- 2.45 (n = 10) in distal myocytes. 4. These findings demonstrate longitudinal differences in Ca2+ channel d ensity and O-2 sensitivity in myocytes along the pulmonary arterial tr ee. These results was help to understand the differential reactivity t o hypoxia of the pulmonary vasculature: vasodilatation in conduit arte ries and vasoconstriction in resistance vessels.