Thiol protease inhibitor imbalance in hearts of dystrophic hamsters

J Mel Cell Cardiol 22 (Supplement

P70

TIiIOL

PROTEASE

I) (1990)

INHIBITOR

IlIBALANCE

IN

HEARTS

OF

DYSTROPHIC

HAMSTERS

Alden H. Warner and Mary A. Ryan, Department of Biological Sciences, University of Windsor, Windsor, ON N9B 3P4 Canada Hamsters of strain CHF-146 have a hereditary form of muscular dystrophy which is expressed in cardiac muscle within 30 days of birth. A recent study of thiol protease regulation in these hamsters revealed the appearance of a thiol protease - thiol protease inhibitor imbalance with age in cardiac muscle. This imbalance was shown to be progressive with age and due to both an increase in cathepsin B activity and reduction in thiol protease inhibitor (TPI) activity. The present study shows that while cardiac muscle of normal 6 month old hamsters contains two major thiol protease inhibitors (TPI-1, TPI-Z), cardiac muscle of age-matched dystrophic hamsters contains only one major thiol protease inhibitor (TPI-1) from a C-18 reverse phase HPLC column. TPI-1 has a higher inhibitor activity towards cathepsin H than B, while TPI-2 has similar inhibitor activity towards these proteases. Our results suggest that the loss of TPI-2 in dystrophic hamster hearts accounts for the overall reduction in TPI activity in this tissue and contributes to the imbalance which occurs in protease/inhibitor activity as these animals age. (Supported by Heart and Stroke Found.)

ENHANCED CALCIUM INTOLERANCE MANIFEST AS AFTERCONTRACTIONS AND VENTRICU-AR FIBRILLATION IN HEARTS OF ACED RAT Osamu Hano, Konstantin Y. Boqdanov, Edward G. Lakatta. Gerontology Research Center, National Institute on Aging,-Baltimore MC 21224 USA. To determine whether myocardial manifest as Ca2+ dependent Ca 24 intolerance, after contractions (AC) or ventricular fibrillation (VF) differ in advanced age, isolated, isovolumic AVblocked hearts from 24-26 mo (0) and 5-7 mo male rats (Y) (n=8 each) were perfused at constant f ow w'th HEWS buffered solution at 37OC in w ich t Ca2+ 1 varied from 1.5M to 1OmM. The [Ca2+ r required for both AC, measured from the pressure recording following cessation of pacing at 2.OH,, and for VF, recorded via surface electrogram and occurring spontaneously during pacing, is reduced in 0 (fig). Note that VF occurs in no Y but in 6 of 8 0 hearts. 2 4 6 8 10 The results indicate that an enhanced likelihooo for PERFUSATE [Caa+] (mM) the occurrence of Ca2+ deoendent abnormalities of

caroiac

P72

cell

CULTURE

function

with

MORPHOLOGY

adult

aging.

DBTERMINBS

ELECTROPHYSIOLOGY

TE

OF

CAT

CARDIOCYTES

Schackow, RS Decker, RE Ten Eick. Northwestern University, Chicago, IL 60611 We have previously reported that the electrophysiological (EP) character of adult cat ventricular myocytes maintained in two-dimensional culture (ZDVM) on laminin-coated coverslips for IO-14 days is different from that of freshly isolated ventricular myocytes (FVM). The morphology of FVM is unchanged from that when in situ, being rod-like, whereas 2DVM develop attachment plaques and spread. The question of whether the altered EP was the result of either culture per se or the change in morphology was addressed by examining myocytes maintained in three-dimensional culture (3DVM) provided by an alginate matrix for a comparable period of time. Action potentials (AP’s) and whole-cell ionic currents were obtained using a conventional whole-cell-patch technique. Quiescent 3DVM were well polarized and elicited AP’s resembling those normally seen in FVM, while quiescent 2DVM were somewhat depolarized and elicited long-duration AP’s which often triggered early afterdepolarizations. Cell capacitance measurements indicated that 3DVM had less membrane surface area than FVM or ZDVM, suggesting that they atrophied while in culture. Peak iR1 current density (current normalized to cell capacitance, IRl) was diminished in ZDVM, and it,, found in most FVM, was rarely elicited by depolarization in either 2DVM or 3DVM. ICa increased in 2DVM and decreased in 3DVM compared with FVM. These data suggest that both culture and morphology are determinants of myocyte EP function. TE Schackow

is a Howard Hughes Medical

Institute

Doctoral

Fellou.

S.24