OPTICAL METHODS TO EVALUATE THE CONTRACTILE FUNCTION OF UNLOADED ISOLATED CARDIAC MYOCYTES

The enzymatically isolated cardiac myocyte has achieved prominence as an experimental model of myocardial excitation contraction coupling, C onsiderable effort has been directed to investigating the shortening b ehaviour of unattached and externally unloaded contracting cardiomyocy tes - measured both at the level of the whole cell and at the level of the sarcomere. The purpose of this review is to provide a survey of t hese methodological approaches and to identify the crucial optical iss ues involved in striation imaging and whole-cell end-detection procedu res. Factors limiting the precision with which measurements of cardiom yocyte shortening can be made, and sources of error attributable to un favourable optical conditions and myocyte geometry are discussed. Orig inal data are presented, examining the relationship between sarcomere and whole-cell shortening dynamics recorded simultaneously in the same cells. These results confirm that the measurement of cell length can provide an adequate index of sarcomere dynamics if the data are obtain ed under carefully controlled conditions where the entire cell is moni tored to ensure minimal geometric or optical non-linearities. The role of the myocyte's internal load in modulating the observed contractile responses at differing levels of inotropic status is discussed. Final ly, the validity of interpreting the shortening response of an untethe red isolated cardiomyocyte as an index of myocardial contractility ref lecting the inotropic status, is considered. (C) 1997 Academic Press L imited.