In coronary artery bypass grafting (CABG), vasospasm of arterial conduits is a significant clinical problem. Unlike the internal mammary artery, the radial artery (RA) is stored in theatre before grafting. Storage induces temperature shocks upon the RA, both following the initial isolation and upon the return of the graft to body temperature. We have studied the effect of temperature changes in native and cultured human RA smooth muscle.
Sections of RA were obtained surplus to CABG, with ethical committee approval. Rings of RA, pretensioned at 30 mN for 1 h, were then relaxed to 10 mN for a further 30 min. RA smooth muscle cells (hRASMCs) were cultured from explants as described previously (Conant et al. 2002) and loaded with fura-2. Data were collected at 37 °C, unless indicated, from at least three separate patients or batches of cells and are presented as means ± S.E.M.
In arterial rings the addition of media at 22 °C to the sample chamber resulted in a transient increase in tension from a basal value of 10.2 ± 0.5 mN to a peak value of 14.6 ± 0.6 mN (n = 29). Glyceryl trinitrate (GTN; 0.5 mg ml-1; 2.2 mM) or 0.5 mg ml-1 (1.5 mM) papaverine prevented this response. In hRASMCs the rapid addition of media at 22 °C led to a transient increase in [Ca2+]c, in 53 % of the cells tested, from a resting value of 221 ± 50 nM (n = 100), to a peak of 315 ± 14 nM. The presence of 1 mM EGTA did not affect the response in either arterial rings or hRASMCs.
In arterial rings gradual cooling to 22 °C led to a slow drop in tension from 15.0 ± 0.6 mN (n = 25) to 11.8 ± 0.5 mN. Subsequent rewarming led to an increase in tension to 26.8 ± 1.6 mN, beyond that of the initial baseline, which was reduced in the presence of GTN, papaverine or EGTA. hRASMCs slowly cooled to 22 °C and then rewarmed to 37 °C showed a rapid and sustained increase in [Ca2+]c from 103 ± 9 to 194 ± 19 nM (n = 144) accompanied by spontaneous [Ca2+]c oscillations in 23 ± 10 % of the cells. The increase in basal calcium was unaffected by GTN or EGTA but calcium oscillations were.
In conclusion the human RA is sensitive to a rapid drop in media temperature. Whilst slower cooling reduces basal tension, subsequent rewarming leads to an increase in tension beyond initial values. These responses are mirrored by changes in [Ca2+]c in cultured hRASMCs. The effects of temperature should be considered during the preparation of the RA for CABG.
All procedures accord with current local guidelines.