Determination of actin content in gallbladder tissue and its relevance to normalization of tensiometry data.

Abstract

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. 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). 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. 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. Normalization of muscle strip force in diseased tissue is questionable, as the assumptions made for healthy tissue are not valid.