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Low PO2 inhibits calcium channel activity in arterial smooth muscle cells
A Franco-Obregón1, J López-Barneo
1Departamento de Fisiología Médica y Biofísica, Facultad de Medicina, Seville, Spain.
Abstract:
We studied the effect of O2 tension (PO2) on the activity of voltage-gated Ca2+ channels recorded in whole cell patch-clamped smooth muscle cells enzymatically dispersed from rabbit cerebral, celiac, femoral, and main pulmonary arteries, as well as from the porcine coronary artery. In all myocyte classes examined, a reduction of PO2 (hypoxia) produced a rapid and reversible inhibition of the macroscopic L-type Ca2+ current of similar general characteristics. The hypoxic inhibition of Ca2+ channel activity closely followed the time course of bath exchange, first becoming apparent at below approximately 80 mmHg PO2. The interaction of O2 with the Ca2+ channels was strongly voltage dependent. At -30 mV the average extent of current inhibition was approximately 80%; however, no effect or even potentiation of current amplitude was observed at potentials more positive than +30 mV. Hypoxia selectively slowed activation kinetics (approximately 1.5 times at -20 mV); however, channel deactivation and inactivation were unaltered by low PO2. In addition, hypoxia produced a reversible shift (8.1 +/- 1.0 mV, n = 12) of the Ca2+ conductance-voltage curve toward positive membrane potentials. We propose that the O2 sensitivity of Ca2+ channels may contribute to the well-known hypoxic dilatation of systemic and the main pulmonary arteries.
Insights
Low oxygen levels (hypoxia) inhibit voltage-gated calcium channels in smooth muscle cells. This oxygen sensitivity may explain how arteries dilate in low-oxygen conditions.
Area of Science:
- Cardiovascular Physiology
- Cellular Electrophysiology
- Respiratory Physiology
Background:
- Smooth muscle cells in arteries regulate vascular tone.
- Voltage-gated calcium channels are crucial for smooth muscle contraction.
- Arterial smooth muscle exhibits complex responses to changes in oxygen tension.
Purpose of the Study:
- To investigate the impact of varying oxygen tension (PO2) on voltage-gated calcium channel activity.
- To determine the role of oxygen in regulating L-type calcium currents in arterial smooth muscle.
- To explore the potential contribution of calcium channel oxygen sensitivity to hypoxic vasodilation.
Main Methods:
- Whole-cell patch-clamp electrophysiology was used to record calcium currents.
- Experiments were conducted on smooth muscle cells from various arteries (rabbit and porcine).
- The effects of reduced PO2 (hypoxia) on calcium channel activity were systematically analyzed.
Main Results:
- Hypoxia rapidly and reversibly inhibited macroscopic L-type calcium currents across all studied cell types.
- Inhibition was observed below approximately 80 mmHg PO2 and was voltage-dependent.
- Hypoxia slowed calcium channel activation kinetics and shifted the conductance-voltage curve positively, without affecting deactivation or inactivation.
Conclusions:
- Oxygen tension directly modulates the activity of voltage-gated calcium channels in arterial smooth muscle.
- The observed oxygen sensitivity of calcium channels provides a potential mechanism for hypoxic arterial dilation.
- These findings link cellular electrophysiology to physiological vascular responses under hypoxia.