INFLUENCE OF HINDLIMB UNWEIGHTING ON PKC LEVELS IN RODENT VENTRICULAR MYOCARDIUM

Adaptations in isoform specific protein kinase C (PKC) expression and activity in left ventricular (LV) myocardium have been associated with the phenomenon of cardioprotection (PKCα, PKCε) as well as cardiac decompensated states such as cardiac failure and aging (PKCβ). Accordingly, we hypothesized that subtype specific alterations in PKC expression would occur in LV myocardium isolated from hindlimb unweighted rats, a model of chronic inactivity. To this end, male sprague-dawley rats (300–350 g) were exposed to hindlimb unweighted (HLU; n = 6) or weight-bearing cast control (CTL; n = 6) conditions for 14 days. LV myocardium was isolated and homogenates were centrifuged and fractionated into cytosolic and particulate cellular fractions. Homogenates were then subjected to western blotting and membranes incubated with polyclonal antibodies for Ca2+-dependent (PKCα, PKCβI, PKCβII), Ca2+-independent (PKCδ, PKC∊) and atypical (PKCξ) PKC isoforms. In the cytosolic cellular fraction, were observed no differences in HLU vs CTL in any of the PKC isoforms measured. Similarly, we observed no differences in particulate PKC levels between experimental groups. In conclusion, these data suggest that under baseline conditions, absolute levels of PKC isoforms are unchanged by HLU in rodent myocardium. These data further suggest that alterations in PKC-dependent cellular effects following HLU may be upstream of PKC and receptor-dependent. Supported by NIH KO1 AG00875 (DHK) and NASA 00-GSRP-045 (WS).