P 568
Investigation of the activation processes of human M. ciliaris and influence of age
T. Noack, S. Hartleib, P. Noack, A. Bacskulin, A. Wree, R. Guthoff
Introduction: Accomodation of the optical apparatus is dramatically changed with increasing age (presbyopia). Changes of the mechanical properties of the lens are one factor governing this problem. Moreover, changes of the smooth muscle, its active mechanical forces could also have changed and are as an additional factor under discussion for this age-related development.
Methods: Human M. ciliaris was collected from routine clinical enucleation. The age of the 10 patients was between 1 and 83 years. The collected tissue was cut into small strip preparations (4 to 6) and these were investigated in relation to their contractile and passive properties.
Results: Using acetylcholine (ACh) as an agonist, the M. ciliaris responded with a long-lasting tonic contraction. Halfmaximal contractions were recorded at [ACh = 10 m M]. The active contractile tension was very small if compared with other smooth muscle preparations ( M. ciliaris: TACh max = 0.3 mN / mm2; gastric fundus: TACh max = 15 mN / mm2). Moreover, M. ciliaris preparations were neither activated by high potassium extracellular solution (20, 40, 80 mM) nor by the L-type calcium channel agonist BAY K 8644 (0.1, 1, 10 m M). This indicates, that the electrical activation processes have no or only little relevance in this tissue. Further investigations using histological techniques demonstrated, that the recorded, small value of maximum tension was due to the small amount (2-3 %) of smooth muscle cells in the tissue compared with gastric muscle (95 %). Data of maximum tension were correlated with the age of the patients. Both, intraindividual and interindividual differences of maximum tension induced by ACh were small. Hence, the correlation was small (r = -0.24) and not significant.
Discussion: Altogether, from this study no evidence can be gained, that presbyopia is effected by smooth muscle dysfunction.
Department of Physiology, University of Rostock, Gertrudenstraße 9, D-18055 Rostock