Effects of cytochrome P-450 inhibitors on ionic currents in isolated rat type I carotid body cells

1996 ◽  
Vol 271 (1) ◽  
pp. C85-C92 ◽  
Author(s):  
C. J. Hatton ◽  
C. Peers
Keyword(s):  
Carotid Body ◽  
Single Channel ◽  
Ionic Currents ◽  
K Channel ◽  
Type I ◽  
Type I Cells ◽  
Channel Inhibition ◽  
Cytochrome P 450 ◽  
I Cells ◽  
K Currents

Hypoxic chemoreception in the carotid body involves selective inhibition of K+ channels in type I cells. We have investigated whether cytochrome P-450 may act as an O2 sensor coupling hypoxia to K+ channel inhibition, by investigating the actions of P-450 inhibitors to modulate channel activity (recorded using patch-clamp techniques) in type I cells isolated from 8-to 12-day-old rat pups. The imidazole antimycotic P-450 inhibitors miconazole and clotrimazole (1-10 microM) inhibited the Ca(2+)-activated (KCa) and voltage-gated K+ (Kv) currents in isolated type I cells. Single-channel recordings indicated that the KCa channels could be inhibited directly by miconazole. Miconazole also irreversibly inhibited Ca2+ channel currents. By contrast, acute application of the suicide substrate P-450 inhibitor, 1-aminobenzotriazole (1-ABT; 3 mM) was without effect on K+ or Ca2+ currents. Hypoxia (16-23 mmHg) reversibly inhibited K+ currents and prevented the inhibitory actions of miconazole. Furthermore, the inhibitory actions of miconazole could be partially reversed by hypoxia. Pretreatment of cells for 60 min with 3 mM 1-ABT substantially reduced the inhibitory actions of hypoxia on K+ currents. Our results indicate that imidazole antimycotic P-450 inhibitors can directly and nonselectively inhibit ionic channels in type I cells but, more importantly, provide evidence to suggest that hypoxic inhibition of K+ currents in type I cells is mediated in part at least by cytochrome P-450.

scholarly journals Low pO2 selectively inhibits K channel activity in chemoreceptor cells of the mammalian carotid body.

1989 ◽  
Vol 93 (5) ◽  
pp. 1001-1015 ◽  
Author(s):  
J López-López ◽  
C González ◽  
J Ureña ◽  
J López-Barneo
Keyword(s):  
Carotid Body ◽  
Action Potentials ◽  
Time Course ◽  
K Channel ◽  
Type I ◽  
Channel Activity ◽  
Type I Cells ◽  
Arterial Blood ◽  
K Current ◽  
I Cells

The hypothesis that changes in environmental O2 tension (pO2) could affect the ionic conductances of dissociated type I cells of the carotid body was tested. Cells were subjected to whole-cell patch clamp and ionic currents were recorded in a control solution with normal pO2 (pO2 = 150 mmHg) and 3-5 min after exposure to the same solution with a lower pO2. Na and Ca currents were unaffected by lowering pO2 to 10 mmHg, however, in all cells studied (n = 42) exposure to hypoxia produced a reversible reduction of the K current. In 14 cells exposed to a pO2 of 10 mmHg peak K current amplitude decreased to 35 +/- 8% of the control value. The effect of low pO2 was independent of the internal Ca2+ concentration and was observed in the absence of internal exogenous nucleotides. Inhibition of K channel activity by hypoxia is a graded phenomenon and in the range between 70 and 120 mmHg, which includes normal pO2 values in arterial blood, it is directly correlated with pO2 levels. Low pO2 appeared to slow down the activation time course of the K current but deactivation kinetics seemed to be unaltered. Type I cells subjected to current clamp generate large Na- and Ca-dependent action potentials repetitively. Exposure to low pO2 produces a 4-10 mV increase in the action potential amplitude and a faster depolarization rate of pacemaker potentials, which leads to an increase in the firing frequency. Repolarization rate of individual action potentials is, however, unaffected, or slightly increased. The selective inhibition of K channel activity by low pO2 is a phenomenon without precedents in the literature that explains the chemoreceptive properties of type I cells. The nature of the interaction of molecular O2 with the K channel protein is unknown, however, it is argued that a hemoglobin-like O2 sensor, perhaps coupled to a G protein, could be involved.

L-type calcium channels in type I cells of the rat carotid body

1993 ◽  
Vol 70 (4) ◽  
pp. 1378-1384 ◽  
Author(s):  
L. A. Fieber ◽  
E. W. McCleskey
Keyword(s):  
Carotid Body ◽  
Single Channel ◽  
Bay K 8644 ◽  
Type I ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Type I Cells ◽  
Voltage Dependent ◽  
I Cells ◽  
Ca2 Channels

1. Whole-cell and cell-attached patch-clamp recordings were made from enzymatically isolated type I cells from the carotid body of adult rats. Voltage-dependent K+ and Ca2+ channels were observed, but there was no detectable Na+ current. In this respect, rat carotid body cells are unlike those from rabbit, which have Na+ currents and Na(+)-dependent action potentials. 2. The observed Ca2+ channels had the following properties: 1) activation requires voltage steps above -20 mV; 2) little inactivation occurred with holding voltages below -40 mV; 3) one single-channel conductance of 21 pS was found with 90 or 110 mM Ba2+ in the cell-attached pipette and this was the only conductance observed; 4) open probability was increased by the dihydropyridine Ca2+ channel agonist Bay K 8644 and was decreased by the antagonist nifedipine; and 5) omega-conotoxin had little or no effect on the channels. These are properties expected of L-type Ca2+ channels. 3. To investigate whether these voltage-dependent channels would be available for opening on membrane depolarization, we measured the type I cell resting membrane potential noninvasively using unitary openings of the L-type Ca2+ channel with Bay K 8644 in the cell-attached pipette. Resting potentials ranged from -62 to -13 mV, with a mean of -32 mV in 12 cells. 4. Judging from single-channel conductance and pharmacology, the Ca2+ current is mostly, if not solely, carried by L channels. Thus it should be possible to use modulators of L channel activity to determine the role of Ca2+ channels in stimulus-secretion coupling in the rat carotid body.

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