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Determination of actin content in gallbladder tissue and its relevance to normalization of tensiometry data
B J Van de Heijning1, A M Van den Broek, H B Luijk
1Department of Gastroenterology, University Hospital Utrecht, The Netherlands.
Objectives:
To compare the common procedure in tensiometry of normalization of the force (in N) produced by a gallbladder tissue strip to units of stress, with normalization of force to the strip content of contractile protein.
Design:
A comparison was made in both healthy and in diseased gallbladder tissue strips between two normalization procedures involving anatomical parameters. The contractile response expressed in terms of tissue stress (in N/m2), which entails a normalization to the strip cross-sectional area, was set against normalization to the tissue content of contractile protein (in N/mg actin/g strip wet weight).
Method:
Dose-response curves for acetylcholine (ACh) (10(-8) to 10(-3) M) and sulphated cholecystokinin octapeptide (CCK) (10(-12) to 10(-6) M) were assessed in healthy guinea pig (n = 8) and in diseased human gallbladder tissue strips (n = 28). Assuming a tissue density of 1.05 g/cm3, the strip cross-sectional area was calculated from its weight and length. Actin content in homogenized strips was determined by polyacrylamide gel electrophoresis followed by densitometry.
Results:
Actin content in human tissue was 19.06 +/- 1.42 mg/g strip wet weight, and 12.84 +/- 0.76 mg/g strip wet weight in guinea pig tissue. No correlation was found between strip cross-sectional area and actin content. In the diseased human tissue, no correlation was found between the inflammation score and either strip cross-sectional area or strip actin content. Maximal force (in mN) exerted in response to either ACh or CCK correlated much more closely in healthy guinea pig gallbladder (r = 0.97) than in diseased human tissue (r = 0.59). Normalization of maximal force to strip cross-sectional area (i.e. to stress) showed considerable more variation (% coefficient of variance) than the normalization to strip actin content in healthy guinea pig tissue, although both strip cross-sectional area and actin content per se showed little variation. Normalization to either parameter did not result in an improved correlation or a decreased variation in the case of diseased human gallbladder tissue.
Conclusion:
Normalization of muscle strip force in diseased tissue is questionable, as the assumptions made for healthy tissue are not valid.