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Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, Spain.

1. Calcium currents were recorded from smooth muscle cells dispersed from conduit and resistance rabbit pulmonary arteries. We tested the hypothesis that Ca2+ channel activity was regulated by environmental O2 tension. 2. Conduit (proximal) and resistance (distal) myocytes differ in their Ca2+ channel density and responses to low PO2. Ca2+ current 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 PO2 is inhibition of the calcium current (n = 12) at membrane potentials below 0 mV, whereas potentiation of current amplitude is observed in distal myocytes (n = 24). 3. Hypoxia also produces opposite shifts in the conductance-voltage relationships along the voltage axis. The average displacements induced by low PO2 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 density and O2 sensitivity in myocytes along the pulmonary arterial tree. These results may help to understand the differential reactivity to hypoxia of the pulmonary vasculature: vasodilatation in conduit arteries and vasoconstriction in resistance vessels.

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