Fig. 5. Heat shock protein accumulation in isolated shark lateral choroid plexus (CP) after zinc exposure in the presence and absence of TMAO. Each lateral CP from an individual shark was divided in half yielding four segments. Paired tissue segments were incubated, ± 72 mmol l^–1 TMAO (13.5°C), with 0 or 50 µmol l^–1 ZnSO₄ for 6 h; all tissues were then incubated in zinc-free medium with TMAO for 1.5 h. (A) Representative immunoblot for Hsp70 and actin accumulation in lysates of zinc-free and zinc-exposed lateral CP. (B) Graphical summation of Hsp70 induction by zinc ± TMAO in lateral CP. Hsp70 accumulation was normalized to that of actin. For zinc exposure with TMAO, fold-induction of Hsp70 was calculated by dividing the normalized Hsp70 accumulation in zinc-treated tissue by that in non-exposed timed-control tissue incubated with TMAO. Likewise, for zinc exposure without TMAO, fold-induction of Hsp70 was calculated by dividing Hsp70 accumulation in zinc-treated tissue by that in non-exposed timed-control tissue incubated without TMAO (means ± s.e.m., N=4; ^*P<0.05 vs fold-induction with TMAO).