Regulation of the resting potential of rabbit pulmonary artery myocytes by a low threshold O2-sensing potassium current

摘要

class="enumerated" style="list-style-type:decimal">The contributions of specific K⁺ currents to the resting membrane potential of rabbit isolated, pulmonary artery myocytes, and their modulation by hypoxia, were investigated by use of the whole-cell, patch-clamp technique.In the presence of 10 μM glibenclamide the resting potential (−50±4 mV, n=18) was unaffected by 10 μM tetraethylammonium ions, 200 nM charybdotoxin, 200  nM iberiotoxin, 100 μM ouabain or 100 μM digitoxin. The negative potential was therefore maintained without ATP-sensitive (KATP) or large conductance Ca²⁺-sensitive (BKCa) K channels, and without the Na⁺-K⁺ATPase.The resting potential, the delayed rectifier current (IK(V)) and the A-like K⁺ current (IK(A)) were all reduced in a concentration-dependent manner by 4-aminopyridine (4-AP) and by quinine.4-AP was equally potent at reducing the resting potential and IK(V), 10 mM causing depolarization from −44 mV to −22 mV with accompanying inhibition of IK(V) by 56% and IK(A) by 79%. In marked contrast, the effects of quinine on resting potential were poorly correlated with its effects on both IK(A) and IK(V). At 10 mM, quinine reduced IK(V) and IK(A) by 47% and 38%, respectively, with no change in the resting potential. At 100 μM, both currents were almost abolished while the resting potential was reduced <50%. Raising the concentration to 1 mM had little further effect on IK(A) or IK(V), but essentially abolished the resting potential.Reduction of the resting potential by quinine was correlated with inhibition of a voltage-gated, low threshold, non-inactivating K⁺ current, IK(N). Thus, 100 μM quinine reduced both IK(N) and the resting potential by around 50%.The resting membrane potential was the same whether measured after clamping the cell at −80 mV, or immediately after a prolonged period of depolarization at 0 mV, which inactivated IK(A) and I_K(V), but not I_K(N).When exposed to a hypoxic solution, the O₂ tension near the cell fell from 125±6 to 14±2 mmHg (n=20), resulting in a slow depolarization of the myocyte membrane to −35±3 mV (n=16). The depolarization occurred without a change in the amplitude of I_K(V) or I_K(A), but it was accompanied by 60% inhibition of I_K(N) at 0 mV.Our findings suggest that the resting potential of rabbit pulmonary artery myocytes depends on I_K(N), and that inhibition of I_K(N) may mediate the depolarization induced by hypoxia.