In vitro intermittent hypoxia: challenges for creating hypoxia in cell culture.
Intermittent hypoxia has been implicated in morbidities associated with sleep apnea, and may be a novel cellular signal for inflammation [J. Appl. Physiol. 90 (2001) 1986]. Standard cell culture has two major limitations for studying the effects of steady-state P(O(2)) and intermittent hypoxia. First, convective mixing in the culture media can be variable, making precise control of cellular P(O(2)) difficult. Second, diffusion of oxygen through the culture media slows changes in cellular P(O(2)) after rapid changes in the gas phase P(O(2)). Our estimates of diffusional transients for standard cell culture suggest significant restrictions in the ability to cycle P(O(2)) at frequencies relevant to intermittent hypoxia. We present a novel system for forced convection cell culture with adherent cells inside capillary tubing. Steady state cellular P(O(2)) is regulated to an accuracy of approximately 1 Torr. The response time for cycling of P(O(2)) is less than 1.6 sec. This system is ideally suited for studies of intermittent hypoxia in adherent cells.