Confocal microscopic localization of constitutive and heat shock-induced proteins HSP70 and HSP27 in the rat heart.

Heat-shock treatment of rats elevates expression of heat-shock proteins, which play a role in improving the contractile recovery and reducing infarct size in hearts after ischemic injury. However, the location of these proteins in the heart is unknown. Anesthetized rats were heat-shocked by elevation of body temperature to 42 degrees C to 42.5 degrees C for 15 minutes, followed by 24 hours of recovery. Control and heat-shocked hearts were extirpated and perfused briefly with saline followed by 2% paraformaldehyde in PBS. Confocal immunofluorescence microscopy of control hearts revealed that HSP27 was localized in cardiomyocytes in a pattern reminiscent of Z bands and was colocalized with neuronal markers in somata and axons. No obvious change in HSP27 content or distribution occurred after heat shock. Confocal microscopy revealed little or no HSP70 in control hearts. After heat shock, HSP70 was detected neither in cardiomyocytes nor in neuronal elements within the heart, but HSP70 was abundant in small blood vessels found between the ventricular cardiomyocytes. Heat shock induces a cell type-specific expression of HSP70 in blood vessels but not myocytes or intrinsic cardiac neurons, suggesting that blood vessels play a primary role in myocardial protection.