OBJECTIVETo investigate changes in adenosine triphosphatase (ATPase) activity and expression of ryanodine receptor 1 (RyR1) mRNA in formation of pressure ulcer at early stage, and to analyze its mechanism.

METHODSThirty-six male Sprague-Dawley rats were divided into three groups according to the random number table as follows, with 12 rats in each group. (1) Ischemia-reperfusion (IR) for 3 times (3IR) group: unilateral gracilis of rats were loaded with 22.47 kPa pressure with a special pressure apparatus for 2.0 h to simulate ischemia, and unloaded for 0.5 h to simulate reperfusion. All rats were treated with above-mentioned manoeuvre for 3 times. (2) IR for 5 times (5IR) group: rats were treated with the same manoeuvre as that in 3IR group except for IR for 5 times. (3) CONTROL GROUP: gracilis of rats were subjected to a load of 0 kPa pressure. Rats in 3IR, 5IR groups were sacrificed, and then central part of pressured tissue was harvested for detection of activity of total ATPase, Ca(2+)-Mg(2+)-ATPase, and Na(+)-K(+)-ATPase with spectrophotometer colorimetry, the level of malondialdehyde (MDA) with enzyme linked immunosorbent assay (ELISA), and the level of RyR1 mRNA with real-time fluorescence quantitative RT-PCR. The same part of gracilis muscle of rats in control group was harvested for determination of indexes as above. Data were processed with one-way analysis of variance. Pearson correlation analysis was respectively performed between total ATPase activity and MDA level, total ATPase activity and RyR1 mRNA expression level, and RyR1 mRNA expression level and MDA level.

RESULTSActivity of total ATPase, Ca(2+)-Mg(2+)-ATPase, Na(+)-K(+)-ATPase in control group was respectively (1.629 ± 0.004), (0.907 ± 0.061), (0.697 ± 0.083) U/mg, all significantly higher than those in 3IR group [(1.365 ± 0.004), (0.784 ± 0.020), (0.581 ± 0.017) U/mg, with F value respectively 1707.0, 29.8, 15.2, P < 0.05 or P < 0.01] and 5IR group [(1.055 ± 0.049), (0.619 ± 0.016), (0.436 ± 0.039) U/mg, with F value respectively 1107.0, 169.9, 65.7, P values all below 0.01], and the values of 3 indexes in 5IR group were obviously lower than those in 3IR group (with F value respectively 322.8, 341.7, 94.0, P values all below 0.01). The level of MDA in control group [(7.5 ± 0.6) nmol/L] was lower than that in 3IR group [(9.9 ± 0.6) nmol/L, F = 53.2, P < 0.01] and 5IR group [(13.7 ± 1.3) nmol/L, F = 76.9, P < 0.01]. There was also statistical difference in MDA level between 3IR group and 5IR group (F = 82.9, P < 0.01). Expression level of RyR1 mRNA in control group (8.5 ± 4.2), which was similar to that in 3IR group (3.3 ± 2.1, F = 0.9, P > 0.05), was significantly higher than that in 5IR group (0.6 ± 0.5, F = 23.6, P < 0.05); while the RyR1 mRNA expression level was lower in 5IR group than in 3IR group (F = 39.3,P < 0.05). Activity of total ATPase was negatively correlated with MDA level (r = -0.918, P < 0.01). Activity of total ATPase was positively correlated with RyR1 mRNA expression level (r = 0.713, P < 0.01). RyR1 mRNA expression level was negatively correlated with MDA level (r = -0.702, P < 0.01).

CONCLUSIONSEnergy dysbolism may be an initial factor in the development of pressure ulcer at early stage. Calcium overload injury in pressure tissue can be identified by determination of RyR1 mRNA expression.