Effects of elastase and collagenase on microelectrode impalements in canine atria at different ages

Mechanical activity in isolated canine atria hinders impalements of single cells with microelectrodes. However, when atrial contractility becomes diminished, a substantial obstacle to impalement remains. To investigate whether the remaining obstacle could be connective tissue, atria were removed from dogs of three age groups (less than 1 year old, 2.8 +/- 0.2 years old and 10.7 +/- 0.5 years old), perfused arterially, and then immersed in elastase (0.01%) or collagenase (0.1%) for 15 min. The following observations were made: (1) In the older atria, satisfactory cell impalements were attained only after they were treated with elastase or collagenase, (2) elastase was effective on the endocardial surfaces only, and (3) collagenase was effective on the epicardial surfaces only. Enzyme effects corresponded to the known anatomic distribution of elastin (endocardial surface) and collagen (epicardial surface). Therefore connective tissue may present a considerable obstacle to cell impalement, especially in hearts from older dogs.