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Lipoprotein lipases (LPL) isolated from rat cardiac muscle and bovine milk were each used as immunogens to produce polyclonal anti-LPL sera and two anti-LPL monoclonal antibodies. The immunological reactivities of these antibody sources with LPL purified from rat cardiac muscle, lung, adipose tissue, mammary gland and skeletal muscle were compared by an e.l.i.s.a. and by Western blotting. Differences between the immunoreactivities of LPL from the distinct tissue sources were revealed in both systems. A synthetic peptide with a sequence corresponding to the heparin-binding site of LPL (Ser-Arg-Thr-Asn-Thr-Lys-Val-Ser-Arg-Ile-Thr-Gly-Leu) was produced and used as an immunogen. The antiserum produced against the synthetic peptide was found to bind specifically to the region of the heparin-binding site, as determined by use of a competition e.l.i.s.a. In use against the five tissue LPL preparations, this antiserum revealed only minor variations between the tissue sources, compared with the hierarchy of reactivity observed when antibodies raised against the whole molecule were used. In combination with the outcome of previous studies on some of the physical properties of these preparations [Soteriou and Cryer (1993) Int. J. Biochem. 25, 1483-1490], the observations reported here on the distinct immunoreactivities exhibited by LPL prepared from the different tissue sources of a single species indicate the necessity to characterize fully the nature of these differences.

It is possible that calmodulin stabilizes the Ca2+-ATPase such that the effects of membrane environment on activity are reduced. No significant difference was seen in T,, for the Ly-.'LPJATP hydrolysis assay in ghost membranes, either in the presence or absence of calmodulin, and may reflect the likely extramembranous location of the ATP hydrolysis site [7]. These results support our previous findings [ 11 that implicate an altered membrane environment in hypertensive animals. An altered membrane environment is further suggested by observations of reduced membrane fluidity [S], reduced sialic acid content [9], abnormal ion transport [lo], altered phosphoinositide turnover [ 111 and CaZ+ binding [ 121 in SHR erythrocyte membranes. Taken together these observations support the hypothesis that an altered membrane environment may be a contributory factor to raised blood pressure in genetic hypertension.

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