Acute hypoxia increases cytosolic calcium in cultured pulmonary arterial myocytes

Abstract

The effects of hypoxia on the cytosolic Ca2+ concentration, [Ca2+]i, were characterized in cultured pulmonary arterial smooth muscle (PASM) cells. Reducing O2 tension (PO2) from 150 to < 25 Torr induced a reversible 100-200% increase in [Ca2+]i that was characterized by two components: an early rise in [Ca2+]i that was dependent on the rate, as well as the magnitude, of decline in PO2 and a later, steady-state increase that was independent of the rate at which PO2 changed. Caffeine lowered [Ca2+]i during normoxia and blocked the early component of the response to hypoxia, whereas the steady-state hypoxic response was only partially inhibited. Like hypoxia, thapsigargin (TG) elevated [Ca2+]i, and there was no additional hypoxia-induced elevation in [Ca2+]i at any time after exposure to TG. At steady state, the hypoxic responses were completely reversed by removal of extracellular Ca2+, whereas, on average, verapamil and nifedipine attenuated the hypoxia-induced increases in [Ca2+]i by only 44 and 35%, respectively. These results suggest that hypoxia-induced elevation of [Ca2+]i in PASM cells consists of an early release of Ca2+ from the sarcoplasmic reticulum and a later influx of extracellular Ca2+, in part, through nifedipine- and verapamil-insensitive Ca2+ channels. The results are consistent with the idea that hypoxia and thapsigargin may share common mechanisms for tonically increasing [Ca2+]i.

Regulation of hypoxic pulmonary vasoconstriction: basic mechanisms

“…Isolated cells were reported to contract in response to a PO 2 of 25-50 mmHg (3.33-6.66 kPa) [26,27], whereas studies with measurement of intracellular calcium were usually performed at PO 2 levels ,30 mmHg (3.99 kPa) [36,106,107]. Integrating these data, it is clear that a sensor must exhibit sensitivity to at least 50 mmHg (6.66 kPa) and below.…”

Relationship between membrane potential, delayed rectifier K+ currents and hypoxia in rat pulmonary arterial myocytes

“…Others have on occasion used a greater degree of hypoxia (8 mmHg; Yuan et al 1994) or added dithionite (e.g. Salvaterra & Goldman, 1993;Yuan et al 1993) to scavenge and reduce PO2 levels in solution in order to obtain depolarization (note that dithionite causes a reduction of 02 with a concomitant production of superoxide anion, which itself has been reported to inhibit vascular reactivity in response to hypoxia (Archer, Hampl, Nelson, Sidney, Peterson & Weir, 1995). Our experiments were also performed in the absence of extracellular Ca2 , thereby obviating the possibility of depolarization being mediated as a consequence of Ca2+ influx through voltage-activated Ca2+ channels.…”

Enhancement of myofilament calcium sensitivity by acute hypoxia in rat distal pulmonary arteries

“…vascular smooth muscle; endothelium; nitric oxide; Rho kinase; temperature; endothelin-1; N -nitro-L-arginine methyl ester; Y-27632 HYPOXIC PULMONARY VASOCONSTRICTION (HPV) is thought to result from an increase in intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) in pulmonary arterial smooth muscle cells (PASMC) (37,40,48,51,52,54,56,62,72,77,82). The increased [Ca 2ϩ ] i leads in turn to calmodulin-dependent activation of myosin light chain (MLC) kinase (MLCK), MLCK-dependent phosphorylation of the 20-kDa regulatory MLC (P-MLC 20 ), P-MLC 20 -dependent activation of the actin-myosin interaction, and PASMC contraction (38,42,74,75,83).…”