This study demonstrates for the first time that endothelial cells freshly isolated from small pulmonary arteries of the rat, based on their electrophysiological profile, possess two distinct populations of cells. Immunohistochemical staining revealed the presence of both anti-Kv1.5 and anti-Kir2.1 immunoreactivity in the endothelium of small pulmonary arteries. Patch-clamp studies demonstrated that 90% of cells studied exhibited an electrophysiological profile that was characterized by a delayed rectifier K+ conductance. However, the remaining 10% of cells studied showed the complete absence of a delayed rectifier K+ current and were characterized by an inward rectifier K+ conductance. Together these results indicate that endothelial cells isolated from rat small pulmonary arteries possess a heterogeneous population of cells that may be distinguished by their markedly different electrophysiological profiles. These different populations of cells may differ in their control of the resting membrane potential of endothelial cells, and thereby altering Ca2+ homeostasis and release of vasoactive compounds. These findings may therefore have important implications for understanding the regulation of pulmonary vascular tone.

These results indicate that K(V)2.1 channel subunits exist within small pulmonary arteries and conduct a significant part of I(KV) within native PASMC. Furthermore, application of AbK(V)2.1 abolishes hypoxic inhibition of I(KV) in native PASMC suggesting that K(V)2.1 channels play a pivotal role in mediating hypoxic pulmonary vasoconstriction.

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1. The effects of clomiphene (CLM) on cardiac outward K+ current components from rat isolated ventricular myocytes were investigated using the whole-cell patch-clamp technique. Clomiphene (10 micromol/L) significantly inhibited both peak (Ipeak) and end-pulse (Ilate) outward currents (elicited by a 500 msec voltage step from -40 to +50 mV in the presence of K+-containing intracellular and extracellular solutions) by approximately 37% (n = 6; P < 0.01) and 49% (n = 6; P < 0.01), respectively. In contrast, CLM had no effect on outward currents when K+-free solutions were used. 2. A double-pulse protocol and Boltzmann fitting were used to separate individual K+ current components on the basis of their voltage-dependent inactivation properties. At potentials positive to -80 mV, two inactivating transient outward components (Ito) and (IKx) and a non-inactivating steady state component (Iss) could be distinguished. 3. Clomiphene inhibited both Ito and Iss. The maximal block of Ito and Iss induced by CLM (100 micromol/L) was approximately 61% (n = 5) and 43% (n = 5) with IC50 values of 1.54 +/- 0.39 and 2.2 +/- 0.4 micromol/L, respectively. In contrast, the peak magnitude of IKx was unaltered by CLM, although its time-course of inactivation was accelerated. 4. Further experiments whereby myocytes were superfused with the vasoactive peptide endothelin (ET)-1 (20 nmol/L) revealed that CLM (10 micro mol/L) completely abolished the ET-1-sensitive component of Iss. 5. Our findings demonstrate, for the first time, the effects of CLM on distinct cardiac K+ current components and show that CLM modulates the voltage-gated K+ current components Ito and IKx and inhibits the steady state outward current Iss in rat ventricular myocytes.

Utilising the patch-clamp recording technique we have demonstrated for the ¢rst time the e¡ects of hypoxia on the background current in pulmonary arterial endothelial cells. Electrophysiological studies revealed the presence of a novel oxygen-sensitive, non-selective cation conductance (I NSC ) in these cells. The inward component of I NSC was signi¢cantly potentiated by hypoxia. Both the inward and outward components of I NSC were inhibited by both La 3+ and Gd 3+ . Hypoxic activation of I NSC may provide an important Ca 2+ in£ux pathway essential for the release of a pulmonary-selective vasoconstrictor pivotal to the sustained phase of hypoxic pulmonary vasoconstriction. ß 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.